I tried this on my own Radeon HD 4870 running on Ubuntu 11.10. I have two of the same monitors Samsung 204B. One cable is DVI and the other is DVI->VGA adapter, and VGA cable into the monitor. After plugging this in, I launched the gnome Displays settings and was able to apply the new settings and get this setup to work.
Looks like this could be related to: https:/ /bugzilla. redhat. com/show_ bug.cgi? id=668196
I tried this on my own Radeon HD 4870 running on Ubuntu 11.10. I have two of the same monitors Samsung 204B. One cable is DVI and the other is DVI->VGA adapter, and VGA cable into the monitor. After plugging this in, I launched the gnome Displays settings and was able to apply the new settings and get this setup to work.