Perhaps this is a bug upstream, but in my opinion important enough to be
mentioned here.
Switching users via gnome menu "switch user" asks for a user name and password.
However when logged in and switched users once, tty2 and tty3 can be switched
without asking for credentials (ctrl+alt+F2 and ctrl+alt+F3).
Only after the gnome energy settings timeout, the screen locks and credentials
are required after switching using tty.
This makes switching users via gnome menu and asking for authentication
pointless.
Switching tty should lock the current gnome session.