Mouse messages arrive at the wrong widgets or not at all

I managed to create a widget setup which screws up completely the messaging system, so that mouse messages arrive at the wrong widgets or not at all.

In the attached example, a complex widget setup can be seen in the file bug.pro.

In a nutshell, the Win widget is embedded in a QStackedWidget and contains as children a push-button and another copy of itself. The children are disabled and have the WA_TransparentForMouseEvents attribute.

What happens is that a click on the push-button does not arrive at the parent Win object. A click on the child Win object arrives at the child even though it is totally disabled.

For the bug to happen, winId() must be called in the Win::Win constructor. Without it everything works correctly.

The example may seem a bit weird, but that's because it comes from a much larger and very complex program.