After updating ubuntustudio 14.04 to current, why can't i reboot/shutdown the system from the logout dialog?

Hello,

I updated my ubuntustudio 14.04 installation to current - this caused several thing to break, among others i can't reboot or shut down my system from the "logout" dialog. Also, the logout/shutdown items in the lightdm login menu (top right of the screen) are greyed out.

I can still shutdown or reboot my machine with shutdown or reboot commands from a terminal or alt+f2 box.