I could be wrong on this, but it seems like if you stun your opponent at the very end of a round it essentially has no effect. The round ends right after your hit and the stun is wiped away at the beginning of the next round. I'm not exactly sure what the best solution is to this, but it seems like the stun should not be tied to rounds and should instead be tied to how many attacks you lose after the stun. So a stun at the end of a round would cause the stunned to lose just as many attacks as a stun at the beginning of a round.
stun.jpg