I'm using recent drivers/kernel/xorg with modesetting and GM45 and most of the time TV-out ends up being detected and set up as active. That confuses GDM and Gnome completely (first won't display across the whole screen, latter doesn't stretch gnome-panel correctly).
The solution would be using xrandr to disable TV1, add a mode to LVDS1
and then switching resolutions once, so that the panel stretches across the whole screen again.
I see that this is a driver bug which in fact doesn't detect TV-out correctly. So I've been wondering lately if there was a way to disable TV-out per default in xorg.conf.