The Player you were specing left the area of the player who recorded the demo (he was to far away) because if u play et ur computer dont calculate / render the whole map ... just the area where you are playing at this moment
to be able to watch another player with wolfcam, he has to be kinda near to you. if he's too far away your demo doesn't have enough information to show his actions i think.
INSELAFFE :p