Comment 10 for bug 641335

@mdz, actually, that's more than helpful, thanks :) I managed to reproduce it and got a good trace. It's because the appmenu is trying to access a window that no longer exists, causing the call to fail and mutter to abort. This bug (appmenu not having good references) is actually a cause of a lot of crashes and is being worked on by jason, so assigning to him.