It sounds like gdm is getting confused by the Virtual keyword in xorg.conf.
IIRC, Virtual was added to support xrandr. Two things need to be researched: A. What this parameter enables. B. Why gdm is getting confused by it.
Also, I suspect there are a number of dupes of this bug (like 139912 possibly) that should be duped together with this one.
It sounds like gdm is getting confused by the Virtual keyword in xorg.conf.
IIRC, Virtual was added to support xrandr. Two things need to be researched: A. What this parameter enables. B. Why gdm is getting confused by it.
Also, I suspect there are a number of dupes of this bug (like 139912 possibly) that should be duped together with this one.