REG [4->5] Windows: Executing a modal dialog using QDialog::exec() launched from timer/event while moving parent window/dialog, freezes mouse buttons

When moving or resizing a window or dialog, and a QMessageBox (or for that matter any other modal dialog) is opened (e.g. via a timer or other event), then the mouse button events won't be noticed anymore, also by the other applications or the OS itself.
This only affects the Windows version, and as far as I could test it, all Qt versions.
The attached application is an example application that was slightly modified: a timer was set-up that pops open a QMessageBox every 5 seconds.