When gdmlogin asks the user for a password, there is no button to 
allow the user to cancel the login process and start over.  It is
necessary to enter an invalid password (or just hit return).
This causes a needless "failed login".  When auditing is enabled,
this means that the audit logs get needlessly filled with failed
logins that could be avoided when the user recognizes that they
mistyped their username, or when they try to enter gdmsetup and
realize they don't know the root password.

Also, from a usability perspective, when the user is presented with
the "enter root password" for entering the setup screen, it isn't
really clear to the user what to do if they don't know the password.
Entering an invalid password to return back to login window does
the job, but the GUI doesn't really make it clear that this is
necessary.

Such situations would be much more clear if the login screen had a
"Cancel" or "Start Over" button.