I can confirm this. Having checked the "Enable accessible login" checkbox that bstqc_ostl mentions, then Quit-->Switch user, it seems to prepare to load the usual GDM greeter, but then immediately switches to the password-protected dialog to return to the session I just quit.
Disabling the accessibility checkbox restores the desired behavior. Marking as confirmed. ** Changed in: gnome-session (Ubuntu) Status: Needs Info => Confirmed -- Lock Screen/Switch User can't use https://launchpad.net/bugs/55575 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs