Guess I'll have to bump the thread so people don't miss it and can offer some help.

As an update to my previous post, I've been told to check if my problems are due to something like making references to the QMdiSubWindows that I close, 'cause then they wouldn't get properly deleted, which could cause the behaviour I'm experiencing. I'll do that later and post again if it solves anything, if only to help others that may come across the same thing.