diff --git a/mail/base/content/mail3PaneWindowCommands.js b/mail/base/content/mail3PaneWindowCommands.js
index af25a5006a..50c69e6f51 100644
--- a/mail/base/content/mail3PaneWindowCommands.js
+++ b/mail/base/content/mail3PaneWindowCommands.js
@@ -310,18 +310,29 @@ var DefaultController =
       case "cmd_viewPageSource":
       case "cmd_reload":
       case "cmd_applyFiltersToSelection":
+        let numSelected = GetNumSelectedMessages();
         if (command == "cmd_applyFiltersToSelection")
         {
           var whichText = "valueMessage";
-          if (GetNumSelectedMessages() > 1)
+          if (numSelected > 1)
             whichText = "valueSelection";
           goSetMenuValue(command, whichText);
           goSetAccessKey(command, whichText + "AccessKey");
         }
-        if (GetNumSelectedMessages() > 0)
+        if (numSelected > 0)
         {
           if (!gFolderDisplay.getCommandStatus(nsMsgViewCommandType.cmdRequiringMsgBody))
             return false;
+            
+          // Check if we have a collapsed thread selected and are summarizing it.
+          // If so, selectedIndices.length won't match numSelected. Also check
+          // that we're not displaying a message, which handles the case
+          // where we failed to summarize the selection and fell back to 
+          // displaying a message.
+          if (gFolderDisplay.selectedIndices.length != numSelected &&
+              command != "cmd_applyFiltersToSelection" &&
+              gDBView && gDBView.currentlyDisplayedMessage == nsMsgViewIndex_None)
+            return false;
           if (command == "cmd_reply" || command == "button_reply" ||
               command == "cmd_replyall" ||command == "button_replyall")
             return IsReplyEnabled();
diff --git a/mailnews/base/public/nsIMsgDBView.idl b/mailnews/base/public/nsIMsgDBView.idl
index 2ece231aa5..bb63646c64 100644
--- a/mailnews/base/public/nsIMsgDBView.idl
+++ b/mailnews/base/public/nsIMsgDBView.idl
@@ -332,7 +332,12 @@ interface nsIMsgDBView : nsISupports
    *  If the "mail.operate_on_msgs_in_collapsed_threads" preference is enabled,
    *  then any collapsed thread roots that are selected will also (conceptually)
    *  have all of the messages in that thread selected and they will be included
-   *  in the returned list.
+   *  in the returned list. The one exception to this is if the front end fails
+   *  to summarize the selection, and we fall back to just displaying a single
+   *  message. In that case, we won't include the children of the collapsed
+   *  thread. However, the numSelected attribute will count those children,
+   *  because the summarizeSelection code uses that to know that it should
+   *  try to summarize the selection.
    *
    * If the user has right-clicked on a message, this will return that message
    *  (and any collapsed children if so enabled) and not the selection prior to
diff --git a/mailnews/base/src/nsMsgDBView.cpp b/mailnews/base/src/nsMsgDBView.cpp
index 02f75e16a1..e33273b31f 100644
--- a/mailnews/base/src/nsMsgDBView.cpp
+++ b/mailnews/base/src/nsMsgDBView.cpp
@@ -163,6 +163,8 @@ nsMsgDBView::nsMsgDBView()
   mSuppressMsgDisplay = PR_FALSE;
   mSuppressCommandUpdating = PR_FALSE;
   mSuppressChangeNotification = PR_FALSE;
+  mSummarizeFailed = PR_FALSE;
+  mSelectionSummarized = PR_FALSE;
   mGoForwardEnabled = PR_FALSE;
   mGoBackEnabled = PR_FALSE;
 
@@ -1047,11 +1049,25 @@ NS_IMETHODIMP nsMsgDBView::SelectionChanged()
       commandsNeedDisablingBecauseOfSelection = PR_TRUE;
   }
   PRBool selectionSummarized = PR_FALSE;
+  mSummarizeFailed = PR_FALSE;
   // let the front-end adjust the message pane appropriately with either
   // the message body, or a summary of the selection
   if (mCommandUpdater)
+  {
     mCommandUpdater->SummarizeSelection(&selectionSummarized);
+    // check if the selection was not summarized, but we expected it to be,
+    // and if so, remember it so GetHeadersFromSelection won't include
+    // the messages in collapsed threads.
+    if (!selectionSummarized &&
+        (numSelected > 1 || (numSelected == 1 &&
+                              m_flags[indices[0]] & nsMsgMessageFlags::Elided &&
+                              OperateOnMsgsInCollapsedThreads())))
+      mSummarizeFailed = PR_TRUE;
+  }
 
+  PRBool summaryStateChanged = selectionSummarized != mSelectionSummarized;
+
+  mSelectionSummarized = selectionSummarized;
   // if only one item is selected then we want to display a message
   if (numSelected == 1 && !selectionSummarized)
   {
@@ -1089,6 +1105,7 @@ NS_IMETHODIMP nsMsgDBView::SelectionChanged()
   // (4) it went from many to 1 or 0
   // (5) a different msg was selected - perhaps it was offline or not...matters only when we are offline
   // (6) we did a forward/back, or went from having no history to having history - not sure how to tell this.
+  // (7) whether the selection was summarized or not changed.
 
   // I think we're going to need to keep track of whether forward/back were enabled/should be enabled,
   // and when this changes, force a command update.
@@ -1098,7 +1115,8 @@ NS_IMETHODIMP nsMsgDBView::SelectionChanged()
 
   NavigateStatus(nsMsgNavigationType::forward, &enableGoForward);
   NavigateStatus(nsMsgNavigationType::back, &enableGoBack);
-  if ((numSelected == mNumSelectedRows ||
+  if (!summaryStateChanged &&
+      (numSelected == mNumSelectedRows ||
       (numSelected > 1 && mNumSelectedRows > 1)) && (commandsNeedDisablingBecauseOfSelection == mCommandsNeedDisablingBecauseOfSelection)
       && enableGoForward == mGoForwardEnabled && enableGoBack == mGoBackEnabled)
   {
@@ -2535,6 +2553,7 @@ PRBool nsMsgDBView::OperateOnMsgsInCollapsedThreads()
     if (!selTree)
       return PR_FALSE;
   }
+
   nsresult rv = NS_OK;
   nsCOMPtr<nsIPrefBranch> prefBranch (do_GetService(NS_PREFSERVICE_CONTRACTID, &rv));
   NS_ENSURE_SUCCESS(rv, PR_FALSE);
@@ -2550,7 +2569,10 @@ nsresult nsMsgDBView::GetHeadersFromSelection(PRUint32 *indices,
 {
   nsresult rv = NS_OK;
 
-  PRBool includeCollapsedMsgs = OperateOnMsgsInCollapsedThreads();
+  // Don't include collapsed messages if the front end failed to summarize
+  // the selection.
+  PRBool includeCollapsedMsgs = OperateOnMsgsInCollapsedThreads() &&
+                                !mSummarizeFailed;
 
   for (PRUint32 index = 0;
        index < (nsMsgViewIndex) numIndices && NS_SUCCEEDED(rv); index++)
diff --git a/mailnews/base/src/nsMsgDBView.h b/mailnews/base/src/nsMsgDBView.h
index 8634348dfb..b89a3178a9 100644
--- a/mailnews/base/src/nsMsgDBView.h
+++ b/mailnews/base/src/nsMsgDBView.h
@@ -445,6 +445,9 @@ protected:
   PRPackedBool mIsNews;             // we have special icons for news
   PRPackedBool mShowSizeInLines;    // for news we show lines instead of size when true
   PRPackedBool m_sortValid;
+  PRPackedBool mSelectionSummarized;
+  // we asked the front end to summarize the selection and it did not.
+  PRPackedBool mSummarizeFailed;
   PRUint8      m_saveRestoreSelectionDepth;
 
   nsCOMPtr <nsIMsgDatabase> m_db;