When any user locks the screen using xlockmore, the screen can be unlocked
with the root password. While root could kill the screensaver process, it
seems a little lax to allow root to unlock the screen. The problem could
potentially be in PAM, I have not looked into this.
That's the normal behavior of xlock, if you're not using
shadow passwords. If you are using shadow passwords, it
can't check the root password.