The 'rule' is - if you are in the public perception, and are in a room with a microphone, assume it is LIVE.
Obama just broke the rule. He said some things which were a little more human than what you'd term Presidential. The message wasn't managed. Other presidents have also been caught.
I know of some guys who were fired for speaking on what they thought was a 'secure' line to a tech at their radio station. Too bad they were on the air over the music on one of the sister stations. Profane and detailed, too.