Comment 24 for bug 216266

I found a workaround! (courtesy of prinknash on ubuntuforums)

Follow it word for word (cut the text.. Apply command change.. paste the text.. Apply command change)

1. Go to System - Administration - Login Window.

2. Under 'General', press "Edit commands ...'

3. Select 'Halt command' - in 'Path' box, cut the text in quotes (I.e. "Shut down via gdm") - press "Apply command change" - paste the text back - press 'Apply command change'

4. Select 'Reboot command' and do as for 3. above

Try restarting a couple of times and see if this has fixed the problem.
Apparently this has fixed the problem for numerous people who have the boot splash but no shutdown splash.
Now, could the solution/workaround give us a possible avenue to explore which might lead to a fix?

I think this makes my first presumption correct. The networkmanager bug has nothing to do with this at all. It's GDM not hiding the error.