During destruction of QWindows there's an unexpected QWindow::visibilityChanged emission which can cause crashes when a slot was connected that uses the window.

I'm attaching an example that is close to what we are seeing in KDE Plasma. We have a derived class of QWindow + some code that connects to visibilityChanged and then touches internals of the derived class. Due to the signal during destruction this leads to accessing already freed resources (the one of the derived class) and ultimately segfaults.