While logged in as a sudo user, click the right top power icon, then select and click Shutdown menu, it comes up with a dialog asking if I want to close all programs. The dialog has two options: restart or shutdown. Choose either one logs me out. Syslog has the following line about restart:
WARNING: Unable to restart system: Authorization is required
This happened after I installed NTP and some OpenStack packages while working in a prototype project. My Ubuntu's software is up to date as of this writing.
Anyone encountered the same problem in 12.04?