I dont visit the duel server much and it might have been suggested somewhere but here it comes:
I was dueling some guy today and after about the 5. hit he went spec so he wont lose, he didnt lose points for doing so. I suggest whenever someone quits a duel the duel is concidered lost for this person.
This should not apply if a duel is interrupted for external reasons, such as a strat battle beginning and players being kicked therefore.