When I go from console mode back to X (ie. alt+F7), my second monitor is black
and nothing will draw on it. I can see the outlines of windows if I move them
over the screen though, but if I release them there they 'disappear'.
I use Xorg 6,8,0 and compositor.
That's an X.org bug - Composite and Xinerama don't seem to play nice.