Well, now that I say that, I tried again after a reboot and sddm loaded a corrupt session, same as gdm3. I'll remove gdm3 as affected.
** No longer affects: gdm3 (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gdm3 in Ubuntu. https://bugs.launchpad.net/bugs/1711936 Title: Severe graphical corruption in gnome-shell with nouveau [Nvidia GeForce 8400M GS] To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1711936/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs