Found something here:
The easy way around it seems to be to add your users to the group 'users', then create a policykit rule to allow users of that group permission to shut down and another to restart when other users are logged in to the system.
[system shutdown privs]
As the top line of each snippet suggests you want to create these files in '/var/lib/polkit-1/localauthority/50-local.d/' with the names 'shutdown.pkla' and 'restart.pkla', so 'sudo gedit', 'sudo kedit', or whatever editor you prefer.
[system restart privs]
If you prefer you can specify individual users who you want to give permission to in the identity line instead of adding them to a group and using the group identity:
Then after the rules are created type:
to activate the rules.
sudo /etc/init.d/hal restart
That still leaves the question as to why the system thinks another user is logged in.