If you press the power button on the login screen, you get a logout dialog from gnome-session. This should be fixed to be the shutdown dialog, but the problem with both dialogs is the same:
They say "You are currently logged in as user 'gdm'".
Thats not a good text for the login screen, we should use the session type to determine if we are on the login screen and show a better text in that case.
Upstream bug has a patch in progress, but it has string changes
We've fixed things as far as we could without string changes (switched to the shutdown dialog).