I think this is a bug, else please move to complaint department.
When you duel, the fight doesn't end with yield/death of one of the parties but only when you log off. I painfully discovered yesterday (luckyily I did it in the DR, and not outside, so the pain was minor).
The logical thing is that the duel ends when one yields or is killed, as it seems to be (DPs are added/substracted and a message apepars saying that X won the duel). Will this be fixed or is it considered a "feature". If the second, I think it's a nonsense.