Well, I was hoping for some self-contained simple-to-reproduce example. I tried grabbing your class and added some basic window creation stuff here
but I don't see the error you are mentioning. If you are able to reproduce the issue by modifying the code above, please post it and we can investigate further.
Apart from this, I would suspect some reference cycle (object A holds reference to object B and object B holds reference to object A - possibly with several objects in between) and that during the app termination this reference cannot be broken and some objects cannot be deinitialized properly.
Best regards,
Jiri
