diff --git a/calendar/base/public/calIICSService.idl b/calendar/base/public/calIICSService.idl
index 7f2c9db7122d..755b46f041f3 100644
--- a/calendar/base/public/calIICSService.idl
+++ b/calendar/base/public/calIICSService.idl
@@ -46,54 +46,60 @@ interface calIIcalProperty;
 [scriptable,uuid(4d7e456b-cfd0-4ebf-8794-c57789dafdc3)]
 interface calIIcalComponent : nsISupports
 {
-    calIIcalComponent getFirstSubcomponent(in PRUint32 componentType);
-    calIIcalComponent getNextSubcomponent(in PRUint32 componentType);
+    /**
+     * This is the value that an integer-valued getter will provide if
+     * there is no such property on the wrapped ical structure.
+     */
+    const PRInt32 INVALID_VALUE = -1;
 
-    const PRUint32 ANY_COMPONENT = 1;
-    const PRUint32 XROOT_COMPONENT = 2;
-    const PRUint32 VEVENT_COMPONENT = 4;
-    const PRUint32 VTODO_COMPONENT = 5;
-    const PRUint32 VJOURNAL_COMPONENT = 6;
-    const PRUint32 VCALENDAR_COMPONENT = 7;
-    const PRUint32 VFREEBUSY_COMPONENT = 8;
-    readonly attribute PRUint32 isA;
+    calIIcalComponent getFirstSubcomponent(in PRInt32 componentType);
+    calIIcalComponent getNextSubcomponent(in PRInt32 componentType);
+
+    const PRInt32 ANY_COMPONENT = 1;
+    const PRInt32 XROOT_COMPONENT = 2;
+    const PRInt32 VEVENT_COMPONENT = 4;
+    const PRInt32 VTODO_COMPONENT = 5;
+    const PRInt32 VJOURNAL_COMPONENT = 6;
+    const PRInt32 VCALENDAR_COMPONENT = 7;
+    const PRInt32 VFREEBUSY_COMPONENT = 8;
+    readonly attribute PRInt32 isA;
 
     attribute AUTF8String uid;
     attribute AUTF8String prodid;
     attribute AUTF8String version;
 
-    const PRUint32 METHOD_PUBLISH = 10012;
-    const PRUint32 METHOD_REQUEST = 10013;
-    const PRUint32 METHOD_REPLY = 10014;
-    const PRUint32 METHOD_ADD = 10015;
-    const PRUint32 METHOD_CANCEL = 10016;
-    const PRUint32 METHOD_REFRESH = 10017;
-    const PRUint32 METHOD_COUNTER = 10018;
-    const PRUint32 METHOD_DECLINECOUNTER = 10019;
-    const PRUint32 METHOD_CREATE = 10020;
-    const PRUint32 METHOD_READ = 10021;
-    const PRUint32 METHOD_RESPONSE = 10022;
-    const PRUint32 METHOD_MOVE = 10023;
-    const PRUint32 METHOD_MODIFY = 10024;
-    const PRUint32 METHOD_GENERATEUID = 10025;
-    const PRUint32 METHOD_DELETE = 10026;
-    const PRUint32 METHOD_NONE = 10027;
-    attribute PRUint32 method;
+    const PRInt32 METHOD_PUBLISH = 10012;
+    const PRInt32 METHOD_REQUEST = 10013;
+    const PRInt32 METHOD_REPLY = 10014;
+    const PRInt32 METHOD_ADD = 10015;
+    const PRInt32 METHOD_CANCEL = 10016;
+    const PRInt32 METHOD_REFRESH = 10017;
+    const PRInt32 METHOD_COUNTER = 10018;
+    const PRInt32 METHOD_DECLINECOUNTER = 10019;
+    const PRInt32 METHOD_CREATE = 10020;
+    const PRInt32 METHOD_READ = 10021;
+    const PRInt32 METHOD_RESPONSE = 10022;
+    const PRInt32 METHOD_MOVE = 10023;
+    const PRInt32 METHOD_MODIFY = 10024;
+    const PRInt32 METHOD_GENERATEUID = 10025;
+    const PRInt32 METHOD_DELETE = 10026;
+    const PRInt32 METHOD_NONE = 10027;
+    attribute PRInt32 method;
 
-    const PRUint32 STATUS_TENTATIVE = 10029;
-    const PRUint32 STATUS_CONFIRMED = 10030;
-    const PRUint32 STATUS_COMPLETED = 10031;
-    const PRUint32 STATUS_NEEDSACTION = 10032;
-    const PRUint32 STATUS_CANCELLED = 10033;
-    const PRUint32 STATUS_INPROCESS = 10034;
-    const PRUint32 STATUS_DRAFT = 10035;
-    const PRUint32 STATUS_FINAL = 10036;
-    const PRUint32 STATUS_NONE = 10037;
-    attribute PRUint32 status;
+    const PRInt32 STATUS_TENTATIVE = 10029;
+    const PRInt32 STATUS_CONFIRMED = 10030;
+    const PRInt32 STATUS_COMPLETED = 10031;
+    const PRInt32 STATUS_NEEDSACTION = 10032;
+    const PRInt32 STATUS_CANCELLED = 10033;
+    const PRInt32 STATUS_INPROCESS = 10034;
+    const PRInt32 STATUS_DRAFT = 10035;
+    const PRInt32 STATUS_FINAL = 10036;
+    const PRInt32 STATUS_NONE = 10037;
+    attribute PRInt32 status;
 
-    const PRUint32 TRANSP_OPAQUE = 10039;
-    const PRUint32 TRANSP_TRANSPARENT = 10040;
-    attribute PRUint32 transp;
+    const PRInt32 TRANSP_OPAQUE = 10039;
+    const PRInt32 TRANSP_TRANSPARENT = 10040;
+    attribute PRInt32 transp;
 
     attribute AUTF8String summary;
     attribute AUTF8String description;
@@ -101,13 +107,13 @@ interface calIIcalComponent : nsISupports
     attribute AUTF8String categories;
     attribute AUTF8String URL;
 
-    attribute PRUint32 priority;
+    attribute PRInt32 priority;
 
-    const PRUint32 VISIBILITY_PUBLIC = 10007;
-    const PRUint32 VISIBILITY_PRIVATE = 10008;
-    const PRUint32 VISIBILITY_CONFIDENTIAL = 10009;
-    const PRUint32 VISIBILITY_NONE = 10010;
-    attribute PRUint32 icalClass;
+    const PRInt32 VISIBILITY_PUBLIC = 10007;
+    const PRInt32 VISIBILITY_PRIVATE = 10008;
+    const PRInt32 VISIBILITY_CONFIDENTIAL = 10009;
+    const PRInt32 VISIBILITY_NONE = 10010;
+    attribute PRInt32 icalClass;
 
     attribute calIDateTime startTime;
     attribute calIDateTime endTime;
@@ -128,13 +134,13 @@ interface calIIcalComponent : nsISupports
     void addSubcomponent(in calIIcalComponent comp);
     void removeSubcomponent(in calIIcalComponent comp);
 
-    const PRUint32 ANY_PROPERTY = 0;
-    const PRUint32 ACTION_PROPERTY = 1;
-    const PRUint32 ATTACH_PROPERTY = 2;
-    const PRUint32 ATTENDEE_PROPERTY = 3;
-    calIIcalProperty getFirstProperty(in PRUint32 kind);
-    calIIcalProperty getNextProperty(in PRUint32 kind);
-    calIIcalProperty addProperty(in PRUint32 kind);
+    const PRInt32 ANY_PROPERTY = 0;
+    const PRInt32 ACTION_PROPERTY = 1;
+    const PRInt32 ATTACH_PROPERTY = 2;
+    const PRInt32 ATTENDEE_PROPERTY = 3;
+    calIIcalProperty getFirstProperty(in PRInt32 kind);
+    calIIcalProperty getNextProperty(in PRInt32 kind);
+    calIIcalProperty addProperty(in PRInt32 kind);
     void removeProperty(in calIIcalProperty prop);
 
     calIIcalProperty getFirstXProperty(in AUTF8String xpropname);
@@ -147,44 +153,44 @@ interface calIIcalComponent : nsISupports
 interface calIIcalProperty : nsISupports
 {
     attribute AUTF8String stringValue;
-    readonly attribute PRUint32 isA;
+    readonly attribute PRInt32 isA;
 
     AUTF8String getXParameter(in AUTF8String xparamname);
     void setXParameter(in AUTF8String xparamname, in AUTF8String xparamval);
     void removeXParameter(in AUTF8String xparamname);
 
-    const PRUint32 ALTREP_PARAMETER = 1;
-    const PRUint32 CN_PARAMETER = 2;
-    const PRUint32 CUTYPE_PARAMETER = 3;
-    const PRUint32 DELEGATEDFROM_PARAMETER = 4;
-    const PRUint32 DELEGATEDTO_PARAMETER = 5;
-    const PRUint32 DIR_PARAMETER = 6;
-    const PRUint32 ENCODING_PARAMETER = 7;
-    const PRUint32 FBTYPE_PARAMETER = 8;
-    const PRUint32 FMTTYPE_PARAMETER = 9;
-    const PRUint32 LANGUAGE_PARAMETER = 10;
-    const PRUint32 MEMBER_PARAMETER = 11;
-    const PRUint32 PARTSTAT_PARAMETER = 12;
-    const PRUint32 RANGE_PARAMETER = 13;
-    const PRUint32 RELATED_PARAMETER = 14;
-    const PRUint32 RELTYPE_PARAMETER = 15;
-    const PRUint32 ROLE_PARAMETER = 16;
-    const PRUint32 RSVP_PARAMETER = 17;
-    const PRUint32 SENTBY_PARAMETER = 18;
-    const PRUint32 TZID_PARAMETER = 19;
-    const PRUint32 VALUE_PARAMETER = 20;
+    const PRInt32 ALTREP_PARAMETER = 1;
+    const PRInt32 CN_PARAMETER = 2;
+    const PRInt32 CUTYPE_PARAMETER = 3;
+    const PRInt32 DELEGATEDFROM_PARAMETER = 4;
+    const PRInt32 DELEGATEDTO_PARAMETER = 5;
+    const PRInt32 DIR_PARAMETER = 6;
+    const PRInt32 ENCODING_PARAMETER = 7;
+    const PRInt32 FBTYPE_PARAMETER = 8;
+    const PRInt32 FMTTYPE_PARAMETER = 9;
+    const PRInt32 LANGUAGE_PARAMETER = 10;
+    const PRInt32 MEMBER_PARAMETER = 11;
+    const PRInt32 PARTSTAT_PARAMETER = 12;
+    const PRInt32 RANGE_PARAMETER = 13;
+    const PRInt32 RELATED_PARAMETER = 14;
+    const PRInt32 RELTYPE_PARAMETER = 15;
+    const PRInt32 ROLE_PARAMETER = 16;
+    const PRInt32 RSVP_PARAMETER = 17;
+    const PRInt32 SENTBY_PARAMETER = 18;
+    const PRInt32 TZID_PARAMETER = 19;
+    const PRInt32 VALUE_PARAMETER = 20;
     /* const PRUint32 X_PARAMETER = 21; */
-    const PRUint32 XLICCOMPARETYPE_PARAMETER = 22;
-    const PRUint32 XLICERRORTYPE_PARAMETER = 23;
+    const PRInt32 XLICCOMPARETYPE_PARAMETER = 22;
+    const PRInt32 XLICERRORTYPE_PARAMETER = 23;
 
-    AUTF8String getParameter(in PRUint32 kind);
-    void setParameter(in PRUint32 kind, in AUTF8String value);
-    void removeParameter(in PRUint32 kind);
+    AUTF8String getParameter(in PRInt32 kind);
+    void setParameter(in PRInt32 kind, in AUTF8String value);
+    void removeParameter(in PRInt32 kind);
 };
 
 [scriptable,uuid(c788a1dc-0929-4029-9a14-e1bc654eafad)]
 interface calIICSService : nsISupports
 {
     calIIcalComponent parseICS(in AUTF8String serialized);
-    calIIcalComponent createIcalComponent(in PRUint32 kind);
+    calIIcalComponent createIcalComponent(in PRInt32 kind);
 };
diff --git a/calendar/base/public/calIItemBase.idl b/calendar/base/public/calIItemBase.idl
index 164a0fae206a..b8dff4513e94 100644
--- a/calendar/base/public/calIItemBase.idl
+++ b/calendar/base/public/calIItemBase.idl
@@ -85,12 +85,15 @@ interface calIItemBase : nsISupports
   // the generation number of this item; 0 means
   // that it's never been stored in a store
   //
-  readonly attribute long generation;
+  readonly attribute PRUint32 generation;
 
   // methods
-  const long CAL_METHOD_NONE = 0;
-  const long CAL_METHOD_PUBLISH = 1;
-  const long CAL_METHOD_REQUEST = 2;
+  const PRUint32 METHOD_PUBLISH = 10012;
+  const PRUint32 METHOD_REQUEST = 10013;
+  const PRUint32 METHOD_REPLY = 10014;
+  const PRUint32 METHOD_ADD = 10015;
+  const PRUint32 METHOD_CANCEL = 10016;
+  const PRUint32 METHOD_NONE = 10027;
 
   // statuses, extended by each event/todo/journal subclass
   const long CAL_ITEM_STATUS_NONE = 0;
diff --git a/calendar/base/src/calICSService.cpp b/calendar/base/src/calICSService.cpp
index 18d97d916ba2..2002cd4d424c 100644
--- a/calendar/base/src/calICSService.cpp
+++ b/calendar/base/src/calICSService.cpp
@@ -74,9 +74,9 @@ protected:
 NS_IMPL_ISUPPORTS1(calIcalProperty, calIIcalProperty)
 
 NS_IMETHODIMP
-calIcalProperty::GetIsA(PRUint32 *isa)
+calIcalProperty::GetIsA(PRInt32 *isa)
 {
-    *isa = (PRUint32)icalproperty_isa(mProperty);
+    *isa = (PRInt32)icalproperty_isa(mProperty);
     return NS_OK;
 }
 
@@ -130,19 +130,19 @@ calIcalProperty::RemoveXParameter(const nsACString &xparamname)
 }
 
 NS_IMETHODIMP
-calIcalProperty::GetParameter(PRUint32 kind, nsACString &value)
+calIcalProperty::GetParameter(PRInt32 kind, nsACString &value)
 {
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
 NS_IMETHODIMP
-calIcalProperty::SetParameter(PRUint32 kind, const nsACString &value)
+calIcalProperty::SetParameter(PRInt32 kind, const nsACString &value)
 {
     return NS_ERROR_NOT_IMPLEMENTED;
 }
 
 NS_IMETHODIMP
-calIcalProperty::RemoveParameter(PRUint32 kind)
+calIcalProperty::RemoveParameter(PRInt32 kind)
 {
     return NS_ERROR_NOT_IMPLEMENTED;
 }
@@ -170,10 +170,12 @@ protected:
     {
         icalproperty *prop =
             icalcomponent_get_first_property(mComponent, kind);
-        if (!prop)
+        if (!prop) {
             str.Truncate();
-        else
+            str.SetIsVoid(PR_TRUE);
+        } else {
             str.Assign(icalvalue_get_string(icalproperty_get_value(prop)));
+        }
         return NS_OK;
     }
 
@@ -185,18 +187,18 @@ protected:
         return SetPropertyValue(kind, val);
     }
 
-    nsresult GetIntProperty(icalproperty_kind kind, PRUint32 *valp)
+    nsresult GetIntProperty(icalproperty_kind kind, PRInt32 *valp)
     {
         icalproperty *prop =
             icalcomponent_get_first_property(mComponent, kind);
         if (!prop)
-            *valp = PR_UINT32_MAX;
+            *valp = calIIcalComponent::INVALID_VALUE;
         else
-            *valp = (PRUint32)icalvalue_get_integer(icalproperty_get_value(prop));
+            *valp = (PRInt32)icalvalue_get_integer(icalproperty_get_value(prop));
         return NS_OK;
     }
 
-    nsresult SetIntProperty(icalproperty_kind kind, PRUint32 i)
+    nsresult SetIntProperty(icalproperty_kind kind, PRInt32 i)
     {
         icalvalue *val = icalvalue_new_integer(i);
         if (!val)
@@ -266,26 +268,26 @@ calIcalComponent::Set##Attrname(const nsACString &str)          \
 
 #define COMP_GENERAL_INT_ATTRIBUTE(Attrname, ICALNAME)          \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Get##Attrname(PRUint32 *valp)                 \
+calIcalComponent::Get##Attrname(PRInt32 *valp)                 \
 {                                                               \
     return GetIntProperty(ICAL_##ICALNAME##_PROPERTY, valp);    \
 }                                                               \
                                                                 \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Set##Attrname(PRUint32 val)                   \
+calIcalComponent::Set##Attrname(PRInt32 val)                   \
 {                                                               \
     return SetIntProperty(ICAL_##ICALNAME##_PROPERTY, val);     \
 }                                                               \
 
 #define COMP_ENUM_ATTRIBUTE(Attrname, ICALNAME, lcname)         \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Get##Attrname(PRUint32 *valp)                 \
+calIcalComponent::Get##Attrname(PRInt32 *valp)                 \
 {                                                               \
     return GetIntProperty(ICAL_##ICALNAME##_PROPERTY, valp);    \
 }                                                               \
                                                                 \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Set##Attrname(PRUint32 val)                   \
+calIcalComponent::Set##Attrname(PRInt32 val)                   \
 {                                                               \
     icalproperty *prop =                                        \
       icalproperty_new_##lcname((icalproperty_##lcname)val);    \
@@ -294,13 +296,13 @@ calIcalComponent::Set##Attrname(PRUint32 val)                   \
 
 #define COMP_INT_ATTRIBUTE(Attrname, ICALNAME, lcname)          \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Get##Attrname(PRUint32 *valp)                 \
+calIcalComponent::Get##Attrname(PRInt32 *valp)                 \
 {                                                               \
     return GetIntProperty(ICAL_##ICALNAME##_PROPERTY, valp);    \
 }                                                               \
                                                                 \
 NS_IMETHODIMP                                                   \
-calIcalComponent::Set##Attrname(PRUint32 val)                   \
+calIcalComponent::Set##Attrname(PRInt32 val)                   \
 {                                                               \
     icalproperty *prop = icalproperty_new_##lcname(val);        \
     return SetProperty(ICAL_##ICALNAME##_PROPERTY, prop);       \
@@ -347,7 +349,7 @@ calIcalComponent::Set##Attrname(calIDateTime *dt)                       \
 NS_IMPL_ISUPPORTS1(calIcalComponent, calIIcalComponent)
 
 NS_IMETHODIMP
-calIcalComponent::GetFirstSubcomponent(PRUint32 componentType,
+calIcalComponent::GetFirstSubcomponent(PRInt32 componentType,
                                        calIIcalComponent **subcomp)
 {
     icalcomponent *ical =
@@ -366,7 +368,7 @@ calIcalComponent::GetFirstSubcomponent(PRUint32 componentType,
 }
 
 NS_IMETHODIMP
-calIcalComponent::GetNextSubcomponent(PRUint32 componentType,
+calIcalComponent::GetNextSubcomponent(PRInt32 componentType,
                                       calIIcalComponent **subcomp)
 {
     icalcomponent *ical =
@@ -385,7 +387,7 @@ calIcalComponent::GetNextSubcomponent(PRUint32 componentType,
 }
 
 NS_IMETHODIMP
-calIcalComponent::GetIsA(PRUint32 *isa)
+calIcalComponent::GetIsA(PRInt32 *isa)
 {
     *isa = icalcomponent_isa(mComponent);
     return NS_OK;
@@ -516,7 +518,7 @@ calIcalComponent::RemoveSubcomponent(calIIcalComponent *comp)
 }
 
 NS_IMETHODIMP
-calIcalComponent::GetFirstProperty(PRUint32 kind, calIIcalProperty **prop)
+calIcalComponent::GetFirstProperty(PRInt32 kind, calIIcalProperty **prop)
 {
     icalproperty *icalprop =
         icalcomponent_get_first_property(mComponent, (icalproperty_kind)kind);
@@ -533,7 +535,7 @@ calIcalComponent::GetFirstProperty(PRUint32 kind, calIIcalProperty **prop)
 }
 
 NS_IMETHODIMP
-calIcalComponent::GetNextProperty(PRUint32 kind, calIIcalProperty **prop)
+calIcalComponent::GetNextProperty(PRInt32 kind, calIIcalProperty **prop)
 {
     icalproperty *icalprop =
         icalcomponent_get_next_property(mComponent, (icalproperty_kind)kind);
@@ -550,7 +552,7 @@ calIcalComponent::GetNextProperty(PRUint32 kind, calIIcalProperty **prop)
 }
 
 NS_IMETHODIMP
-calIcalComponent::AddProperty(PRUint32 kind, calIIcalProperty **prop)
+calIcalComponent::AddProperty(PRInt32 kind, calIIcalProperty **prop)
 {
     icalproperty *icalprop = icalproperty_new((icalproperty_kind)kind);
     if (!icalprop)
@@ -664,7 +666,7 @@ calICSService::ParseICS(const nsACString& serialized,
 }
 
 NS_IMETHODIMP
-calICSService::CreateIcalComponent(PRUint32 kind, calIIcalComponent **comp)
+calICSService::CreateIcalComponent(PRInt32 kind, calIIcalComponent **comp)
 {
     icalcomponent *ical = icalcomponent_new((icalcomponent_kind)kind);
     if (!ical)
diff --git a/calendar/base/src/calItemBase.js b/calendar/base/src/calItemBase.js
index 069752d90f9b..1c3d8731ba14 100644
--- a/calendar/base/src/calItemBase.js
+++ b/calendar/base/src/calItemBase.js
@@ -96,8 +96,8 @@ calItemBase.prototype = {
     mTitle: "", get title() { return this.mTitle; }, set title(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mTitle = v; },
     mPriority: 0, get priority() { return this.mPriority; }, set priority(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mPriority = v; },
     mIsPrivate: 0, get isPrivate() { return this.mIsPrivate; }, set isPrivate(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mIsPrivate = v; },
-    mMethod: 0, get method() { return this.mMethod; }, set method(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mMethod = v; },
-    mStatus: 0, get status() { return this.mStatus; }, set status(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mStatus = v; },
+    mMethod: ICAL.INVALID_VALUE, get method() { return this.mMethod; }, set method(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mMethod = v; },
+    mStatus: ICAL.INVALID_VALUE, get status() { return this.mStatus; }, set status(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mStatus = v; },
     mHasAlarm: false, get hasAlarm() { return this.mHasAlarm; }, set hasAlarm(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mHasAlarm = v; },
     mAlarmTime: null, get alarmTime() { return this.mAlarmTime; }, set alarmTime(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mAlarmTime = v; },
     mRecurrenceInfo: null, get recurrenceInfo() { return this.mRecurrenceInfo; }, set recurrenceInfo(v) { if (this.mImmutable) throw Components.results.NS_ERROR_FAILURE; else this.mRecurrenceInfo = v; },
@@ -170,23 +170,26 @@ calItemBase.prototype = {
     mapPropsFromICS: function(icalcomp, propmap) {
         for (var i = 0; i < propmap.length; i++) {
             var prop = propmap[i];
-            this[prop.cal] = icalcomp[prop.ics];
+            var val = icalcomp[prop.ics];
+            if (val != ICAL.INVALID_VALUE)
+                this[prop.cal] = val;
         }
     },
 
     mapPropsToICS: function(icalcomp, propmap) {
         for (var i = 0; i < propmap.length; i++) {
             var prop = propmap[i];
+            if (!(prop.cal in this))
+                continue;
             var val = this[prop.cal];
-            if (prop.force || val)
-                icalcomp[prop.ics] = this[prop.cal];
+            if (val != null && val != ICAL.INVALID_VALUE)
+                icalcomp[prop.ics] = val;
         }
     },
 
     icsBasePropMap: [
     { cal: "mCreationDate", ics: "createdTime" },
     { cal: "mLastModifiedTime", ics: "lastModified" },
-    { cal: "mGeneration", ics: "version" },
     { cal: "mId", ics: "uid" },
     { cal: "mTitle", ics: "summary" },
     { cal: "mPriority", ics: "priority" },
diff --git a/calendar/base/src/calItemBase.js.pre b/calendar/base/src/calItemBase.js.pre
index a80e855ed86e..e979bd29c072 100644
--- a/calendar/base/src/calItemBase.js.pre
+++ b/calendar/base/src/calItemBase.js.pre
@@ -138,8 +138,8 @@ calItemBase.prototype = {
     MEMBER_ATTR(mTitle, "", title),
     MEMBER_ATTR(mPriority, 0, priority),
     MEMBER_ATTR(mIsPrivate, 0, isPrivate),
-    MEMBER_ATTR(mMethod, 0, method),
-    MEMBER_ATTR(mStatus, 0, status),
+    MEMBER_ATTR(mMethod, ICAL.INVALID_VALUE, method),
+    MEMBER_ATTR(mStatus, ICAL.INVALID_VALUE, status),
     MEMBER_ATTR(mHasAlarm, false, hasAlarm),
     MEMBER_ATTR(mAlarmTime, null, alarmTime),
     MEMBER_ATTR(mRecurrenceInfo, null, recurrenceInfo),
@@ -212,23 +212,26 @@ calItemBase.prototype = {
     mapPropsFromICS: function(icalcomp, propmap) {
         for (var i = 0; i < propmap.length; i++) {
             var prop = propmap[i];
-            this[prop.cal] = icalcomp[prop.ics];
+            var val = icalcomp[prop.ics];
+            if (val != null && val != ICAL.INVALID_VALUE)
+                this[prop.cal] = val;
         }
     },
 
     mapPropsToICS: function(icalcomp, propmap) {
         for (var i = 0; i < propmap.length; i++) {
             var prop = propmap[i];
+            if (!(prop.cal in this))
+                continue;
             var val = this[prop.cal];
-            if (prop.force || val)
-                icalcomp[prop.ics] = this[prop.cal];
+            if (val != null && val != ICAL.INVALID_VALUE)
+                icalcomp[prop.ics] = val;
         }
     },
 
     icsBasePropMap: [
     { cal: "mCreationDate", ics: "createdTime" },
     { cal: "mLastModifiedTime", ics: "lastModified" },
-    { cal: "mGeneration", ics: "version" },
     { cal: "mId", ics: "uid" },
     { cal: "mTitle", ics: "summary" },
     { cal: "mPriority", ics: "priority" },