Created attachment 32607 [details]
Server log with "stock" driver

Driver version: 6.12.4 (Debian unstable packages)
Kernel: Linux 2.6.32.3 (stock)

This may be related to http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=550637

The issue is that with DRI enabled and two monitors connected (HDMI and DVI) (no matter whether running mirrored or some separate layout), drawing operations anywhere on the screen cause short-lived corruption. It looks like partial lines are replaced with uninitialized memory. This happens in KDE and Gnome, with or without acceleration, as long as DRI is not disabled in the xorg.conf. It seems like the effect is most severe on pixel rows where some changes occur.

I tried the setting DisplayPriority option to HIGH as mentioned in the Debian bug report, but that did no good.

The effect does not seem to occur in current git master, but there I get different issues, making the whole thing unusable. It seems that screen sizes get mixed up, so that the screen doesn't get drawn properly. I have a 1920x1200 display in landscape mode, and a 1600x1200 display in portrait to the right of it. When setting that up with the xrandr tool or the Gnome display tool, the left monitor has a picture that seems to be only 1200 pixels wide stuck to the left, while the right of the screen is black, but the mouse pointer moves into the area. At some point, the driver appeared to forget about the right monitor altogether, displaying only a background image and a functional mouse pointer. Windows on that screen still seem to be there, since the pointer changes shapes. During some attemps, I also experienced serious mouse pointer corruption.

None of those effects occur when only physically connecting a single monitor; Both the 6.12.4 and the git master drivers work fine then.