My current investigation indicates the issue is related to the Ubuntu custom login/logout dialog.
Specifically, the 13_smoother_fading patch. I'm still investigating, but I believe it is related to the time jumping during the fade event. *grumbles about how bloated gnome-session has become* -- Unable to start applications after suspend/hibernation https://launchpad.net/bugs/49221 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs