It's still an issue in Jaunty, whether via the Fast User Switch applet or via System/Log out/Switch user, with the same steps.
1. Login as User A
2. Switch user to User B
3. Log out of User B
4. (expected) Type User A's password and click Unlock
(actual) Type User A's password and press Shift+Tab, Enter or Meta+U, because the Unlock button cannot be clicked