OK, this seems to be a Xorg bug in the "-background none" feature. Upstream bug reported here: https://bugs.freedesktop.org/show_bug.cgi?id=105518
Less likely but still possible is that mutter (used on the login screen) is corrupting the framebuffer and "Xorg -background none" is then innocently copying the corruption. A workaround (which at least will avoid more bug reports from users) is to remove these two lines from gdm3: g_ptr_array_add (arguments, "-background"); g_ptr_array_add (arguments, "none"); That will reliably replace the corruption with blackness. Have a nice day. ** Bug watch added: freedesktop.org Bugzilla #105518 https://bugs.freedesktop.org/show_bug.cgi?id=105518 ** Also affects: xorg-server via https://bugs.freedesktop.org/show_bug.cgi?id=105518 Importance: Unknown Status: Unknown -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to mesa in Ubuntu. https://bugs.launchpad.net/bugs/1753776 Title: Graphics corruption (or distortion?) in login animation to Xorg sessions To manage notifications about this bug go to: https://bugs.launchpad.net/xorg-server/+bug/1753776/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp