The fuckup is usually in the interface between the keyboard and the chair.
I would say always. If the fuckup is in my office please let me know.

The QMainWindow has by default the child QRubberband (by default not visible and disables). It's objectname is qt_rubberband. In our application. It is blocking events in the upper left corner.

If I'm stuck with the same problem one more houre I will go into the details...

Andreas