Bug#567318: Longer session
Here is a longer set of experience to help track the dirty pointer.
Initial situation: both LVDS and VGA on when starting X.
launching gnome-screensaver: fading on LVDS, not on VGA.
xrandr --output LVDS --off --output VGA --auto
xrandr -q (without it, as said before, it crahes)
fading on VGA
xrandr --output LVDS --auto
fading on VGA, not on LVDS (no crash)
fading on LVDS, not on VGA