Always emit an explicit method override if we've mangled the name/sig, because we can't predict whether it will be needed or not (without keeping track of the mangling in the base classes) and the cost is minimal since this doesn't happen all that often.

runtime/TypeWrapper.cs

@@ -6177,7 +6177,7 @@ namespace IKVM.Internal
 									setNameSig = true;
 								}
 							}
-							bool needMethodImpl = baseMce != null && (explicitOverride || baseMce.RealName != name) && !needFinalize;
+							bool needMethodImpl = baseMce != null && (setNameSig || explicitOverride || baseMce.RealName != name) && !needFinalize;
 							if(unloadableOverrideStub || needMethodImpl)
 							{
 								attribs |= MethodAttributes.NewSlot;