Fixed: if CPArrayController setPreserveSelection was off and a selected item disappeared, an invalid selection state could occur. The error was caused by a slightly overeager early-out optimisation in __setSelectionIndexes.

AppKit/CPArrayController.j

@@ -363,9 +363,6 @@
     if (!indexes)
         indexes = [CPIndexSet indexSet];
 
-    if ([_selectionIndexes isEqualToIndexSet:indexes])
-        return NO;
-
     if (![indexes count])
     {
         if(_avoidsEmptySelection && [[self arrangedObjects] count])
@@ -381,6 +378,9 @@
             indexes = [CPIndexSet indexSetWithIndex:objectsCount-1];
     }
 
+    if ([_selectionIndexes isEqualToIndexSet:indexes])
+        return NO;
+
     _selectionIndexes = [indexes copy];
 
     // Push back the new selection to the model for selectionIndexes if we have one.