[Reg 6.4.3->6.5] Application window not active after closing message box

• build & run the standarddialogs example
• click e.g. Message Boxes > QMessageBox::critical
• press e.g. escape to close the dialog
• notice that the standarddialogs window is not active, e.g. by the missing colors in the window decoration buttons
• press <escape> or other keys: The keys result in a beep, the keys are not delivered to the standarddialogs window

Expected: After closing the message box the window should get the active state back and receive key events

In Qt Creator this is noticeable after a message box opens and then trying to type anything.