Putting this under linux-restricted-modules, as I suspect it's related to fglrx.
Re-opening, because I see the same thing in Hardy, using kwin-kde4 with compositing features enabled. I suspect that it may be related to 3d acceleration, hence why Alexei found it didn't occur with metacity.
Kubuntu-KDE4 Hardy, ATI Mobility Radeon X600 with fglrx drivers from repositories (hardy-backports).
Putting this under linux-restricte d-modules, as I suspect it's related to fglrx.
Re-opening, because I see the same thing in Hardy, using kwin-kde4 with compositing features enabled. I suspect that it may be related to 3d acceleration, hence why Alexei found it didn't occur with metacity.
Kubuntu-KDE4 Hardy, ATI Mobility Radeon X600 with fglrx drivers from repositories (hardy-backports).