gnome shutdown no longer asks for root password

[Nick Dreyer <gurfle@oz.net>]

When I initially got my gnome desktop up and running (default debian 3.1r1
install), I was glad to see that it would not let you shut the system down
without asking for root's password.

Something has happened since then - I have no idea what - that causes the
shutdown sequence to start of immediately when initiated from a desktop
session (Actions --> Log Out --> Shut down) without requiring root's
password.

Can anyone help me find out what happened, and how to restore the (to me)
important shutdown password security measure?

Thanks so much in advance for your help.

Nick