I'm using an NSOutlineView with the function

- (BOOL)outlineView:(NSOutlineView *)outlineView
  isGroupItem:(id)item

defined so it gives the group row GUI look. When I add a root item, it works fine. When I add an item to root's child array and expand it, it works fine. If I contract the item though, the following error is logged:

[NSCFTimer copyWithZone:]: unrecognized selector sent to instance

I also get an EXC_BAD_ACCESS error if the app window is deactivated by switching to another app. I used the debugger to try to find where I might have made an error in one of my functions, but the stack trace only shows functions I did not create (RunCurrentEventLoopInMode, CFRunLoopRunSpecific, handleWindowNeedsDisplay, etc.) Does anyone have any idea where my error(s) might be?