OS is telling you that window has been moved, not will be moved, so there's nothing to prevent any more.
After that it also asks Qt to kindly repaint the window so it won't look bad.
See the bold quote.
That is the point though.
As long as Qt did not repaint the window, you will still see it in the old position - even though the OS has moved it logically - on the screen it still didn't move.
If you intervene at this time - tell Qt to move the window back to the old position - before it painted it in the new - OS triggered position, the window will *appear* not to have moved.

It may be possible to overcome the move, but as far as I know it's impossible to do it using Qt only.
In this case Qt is being pushed around by OS so you have to go down to the native api level to do something with it.
Well, I will test that.
It might be true that one will have to catch WM_MOVE or similar, but that is not much, to have #ifdef with variants for other windowing systems - but that is something I still have to prove :-)

to be continued...