could you attach your /etc/gdm/gdm.conf and /etc/gdm/gdm.conf-custom to the bug (feel free to replace any user name or data you think should not be on the bug tracker by random chars by example)
could you attach your /etc/gdm/gdm.conf and /etc/gdm/ gdm.conf- custom to the bug (feel free to replace any user name or data you think should not be on the bug tracker by random chars by example)