Images are worth thousands of words so I made a video of the issue: https://www.youtube.com/watch?v=4xPJpiAFGEY .

I did a fresh install of Debian 7.6. Everything went fine. This particular machine has a discrete ATI Radeon 5460 graphics card. At first boot the monitors were mirrored but all else was fine (system detected the card: lspci showed that). So I downloaded the latest stable ATI catalyst drivers and installed it. The installer detected the card, and the generic drivers were installed without issue. Rebooted and everything was fine.

The Display application (and the catalyst control panel) showed two monitors and I could change resolution on them and what not.

The only problem is, the secondary monitor is not refreshing unless I click something on the system bar along the top there. That's not entirely true -- I can see the location of the cursor and the cursor change from a pointer to the hand when moving the window.

I've tried uninstalling the drivers and re-installing them. I've tried installing the beta drivers, etc - no luck. I haven't had luck with installing distribution-specific drivers (running --buildpkg Debian/stable , crashes with a bunch of stuff about not finding the required tools).

Thanks for the help

Have you created a new /etc/X11/xorg.conf file & edited it manuall?
You have to stop DM & then emter command "X -configure" then move to /etc/X11/xorg.conf

Oh... boy. I re-read the documentation and it says run aticonfig post installation. I originally thought it would run it automatically. Sorry. Let me try this tomorrow on my workstation and post my results here.

Thanks so much.