I had a similar experience over the weekend at a concert. There was a woman seated in front of me who sat down the entire first half of the show. In the second half of the show she stood up for the entire rest of the show. She hardly moved a muscle though except to occasionally toss her head. It was weird that she just stood there nearly motionless. It didn't really bother me because the act was to the right of her but the guy beside me was blocked off.