It seems like you have dbus installed. I don't know what the precedence is, but AFAIK dbus can be used to initiate the shutdown. Have you changed anything there? Maybe you can check if dbus is running when it asks for a password, and when it doesn't?
~David -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]