Wallpaper Fragments in Launchpad, howto fix?

Hi ASC,

I frequently end up with an unusable Launchpad b/c my internal display wallpaper will overlay.

The rhino is the actual wallpaper on this screen and the other one is set on my MBPr screen.

Howto Reproduce:

1. Connect external Display to MBPr
2. Close lid.
3. Bug!

If I then open the lid with MBPr as main screen, the Problem disappears (no fragment on any display in Launchpad).

After closing the lid again, the bug reappears on the external (main) display.

This error is present the whole time I was using the MBPr and is no 10.8.4 regression!

Anyone else with this problem?

Best regards,

dr0pi