Unsportsmanlike Conduct penalty - Bench?

During the NE-BAL game on Sunday 10/04/09, there was a penalty called for "Unsportsmanlike Conduct - Baltimore Bench". The TV announcers stated that they had never heard of that penalty or even recall when it was ever used before. Could someone explain this one a bit? I looked over the NFL rules, and there was nothing specific about it either. Thank you...