Same Game example becomes unplayable

1. Start the Same Game example (examples\quick\demos\samegame\samegame.pro).
2. Enter "Puzzle" mode.
3. Proceed until you see the start screen for level 3:
   
4. Click several times very quickly into the window.
   The background of the game becomes the same as the foreground. It's nearly impossible to spot which puzzle piece is part of the background and which piece is part of the game.
5. Click on the "Menu" button.
   The menu also has the changed background:
   

The background of the game should not change just because someone clicks quickly. Might this even point to an issue in the underlying Qt code?

Found by Henri.