Well, the full story comes out on B.J. Penn and his third round in UFC 63.
Seems he separated a rib. His own site got the exclusive. Barring an out-right lie, it would explain why a person who used his flexibility through two rounds to escape, couldn’t do the same from a simple crucifix position. This is definitely going to force me to go home and watch for B.J. Penn’s facial expressions closely in that round to help me determine whether this was true or not...