Problem:

Mnemonics are not displayed after 'Alt' key press in basic Qt widgets. They appear when you put mouse over them, and never disappear. I saw some other different mnemonics bugs for version Qt 4.x and 5.x, and some problems still occur in newest Qt Creator 17.0 and Qt 6.9.1 (MSVC 2022, x86_64) version.

How to reproduce it:

1. Create basic window application with 3 buttons, where each of them have assign mnemonic.
2. Put mouse somewhere on frame and press any mnemonic shortcut
3. Underscore sign should appear under each mnemonic letter to inform user about available shortcuts, but nothing such happen.
4. Even if you use previous define shortcut e.g. 'Alt' + 'O' for Open, mnemonic appear, but then never disappear.

Hints and tips:

Take a look on my minimal reproducible example, which I attached to this ticket. When you uncomment function repaint() in MainWindow::keyPressEvent, you should solve the first error, but the same approach in MainWindow::keyReleaseEvent doen't hide the mnemonics on QPushButtons. Alt modifiers look and behave fine, so probably, state is not correctly propagate to widgets in QWindow.