Comment 13 for bug 533784

Seeing this as well, running xbmc initially, but tested with extreme-tuxracer with the same effects.

Environment:
gentoo x86 2.6.31-gentoo-r6
media-tv/xbmc-9.11-r1 (Confluence skin, no unusual plugins/scripts)

01:00.0 VGA compatible controller: ATI Technologies Inc RV370 5B60 [Radeon X300 (PCIE)]

media-libs/mesa-7.5.2
x11-base/xorg-server-1.6.5-r1
x11-drivers/xf86-video-ati-6.12.4
x11-libs/libdrm-2.4.15