This used to work some time ago. I could connect a second screen on the display port interface of my laptop (via display port -> DVI adapter), then use the catalyst control center and select "Single Display Desktop (Multi-Desktop)" to have an extended desktop where I can work with my laptop screen and the seperate screen side by side.
Initially when I connect the display I get cloned desktop mode. Now when I go to catalyst and select said option, I get the usual "do you want to keep these settings" message for 15s. At this point I can already see that nothing changed (which used to be different). I get a message asking me to restart the machine in order to make the changes work. This wasn't necessary before.
After a restart when the gnome desktop has loaded, I have
- one display with white background and two empty gnome-panels, one on top and one on the bottom - nothing else (there is the usual desktop context menu on right click though)
- The other display has the usual look and panels, except every item on the panel is duplicated, i.e. two application/places menues two clocks two system menus two taskbars, two workspace switchers etc.
- I can move the mouse cursor across the screens seamlessly, I cannot drag windows from one screen to the other.
Also interestingly the window switcher normally displays a 2-by-2 workspace layout. Now suddenly I have 1-by-4 (single row). The workspace switcher used to visualise the additional screen real-estate
In short the desktop is totally messed up. I can't begin to express how annoying this is.
Ubuntu version is 12.04, I do not use the unity ui, but the classic gnome one.