TK402 (Sy) ticked off Lord Vader just one-too-many times. Other Stormtroopers initially ran to help him out... Sy, not Vader... Then, they realized they were just stepping in the queue. The next shot in this scene featured Vader, Sy (on the floor resting with the Rebels) but the Stormtroopers are gone... They uhhh, bravely turned around and uhh, found another battle to fight.