Missunderstanding is possible, It happens to me quite often

I'm guessing that you assume that every qt window is always moved using QObject::move(), which generates the moveEvent().
That's largery true, except when OS is moving the window using native api (can happen in few scenarios). QObject::move() is never called and only thing that Qt does, it uses the windows event to update it's internal data about window position.

Anyway, try it, if you find anything how to stop the window from being moved via titlebar using Qt (as per OP's question) let me know, it may come handy