Today we found two oddities on the teacher stations:

1. A teacher logged in to the Lab B machine could not log out, although he could shut the machine down or restart it. Any non-admin logging in was in the same position. You could choose Log Out, but nothing happened as a result.
2. In Lab C, where the machine had never been logged in all day, it was impossible to shut it down without logging it in.

I deduce that when these machines are first started, before they've been logged in, they can't be shut down from the login screen because servers probably shouldn't be shut down by anyone at will. That's logical for servers, but a bit annoying in this context. The other problem is odd. If there should be any restriction at all on low-privilege users, it should be that they can't shut the machine down, not that they can't log off; we want them to log off. And in any case, they can achieve logging off simply by restarting.

Posting minutes spent testing this in the two labs.