QMessageBox doesn't receive mouse events if it pops up while mouse button is pressed

If a QMessageBox is shown when mouse button is pressed the message box is not receiving any mouse events and therefore user cannot click any buttons in the message box. The message box accepts key events normally.

In the attached example the message box is triggered when a dockwidget is dragged. The mouse events go to QDockWidgetClassWindow and they never reach the message box. When the message box is accepted (using keyboard) the dockwidget keeps following the mouse like being dragged still even if the mouse button is not pressed anymore.

The problem is reproducible at least in Windows and in Linux. The behavior is a little different in the OSs: in Linux the dockwidget needs to be floating to reproduce the problem.

This might be related to bug: https://bugreports.qt-project.org/browse/QTBUG-26100, which has a similar behavior, but different use case.