Comment 9 for bug 967229

So there is a bug here with upstart, but I think it's more subtle than what you describe. There's really no strict ordering of any of the jobs at shutdown time, *except* that the plymouth splash screen is started immediately after lightdm exits. Delaying the shutdown of all other services (including /etc/init/rc.conf) until after lightdm has exited would be cumbersome and potentially fragile.

Instead, I think there are two things that need to be done here:
 - the screen needs to be cleared behind lightdm when it *starts*; this way, any start-time noise (which accounts for at least most of what's on the screen in the video attached to the original report) is gone. This impacts not only shutdown, but also any X server restarts/crashes; we shouldn't show garbage then either. This should probably be done in the lightdm job.
 - if possible, plymouth should start *before* lightdm stops on shutdown, putting its redirection of console output in place before any scripts have a chance to output to the console. This way the shutdown scripts are able to keep on running, and are just prevented from messing up the screen.