If I create window and call winId() in window constructor for any widget on this window, this will lead to incorrect behavior of any mouse events for any widgets on this window.

It seems to

event->globalPos()

is not equal to

mapToGlobal(event->pos())

mapToGlobal(event->pos()) always return correct position.

The attached file contains simple example with context menu.

P.S. In my case It reproduces only on 4k monitor if this monitor is not primary.