Just found something strange after updating from 10.04 to 10.10. I've set up my screensaver to lock the account when activated.
When I log back in, I see my desktop for a second and then the screensaver starts again and I have to re-login. I checked my process list in gnome system monitor, and I have two gnome-screensaver processes(!?), one started as /usr/bin/gnome-screensaver and other simply as gnome-screensaver. And no, I did not start one manually.
Where do I look for a way to switch off one of those (supposing that's the problem)? I did not find anything in my startup applications.
As suggested by DoR, a restart seems to have resolved the issue permanently.