The problem is really BIG. And not only for people like my, which want to have gdm or other login screen on DVI instead of TV (used only for watching movies). It is problem for power users with DVI and CRT plugged simultaneously. For example, one want to have 3D modeler on DVI with sharp lines and secondary CRT for OpenGL preview of the 3D model.
I posted about this problem more than half year ago and somebody replied that it is hardware problem
It is nonsense while same gfx card under windows can use DVI as primary nad TV as secondary screen.