I downed and captured a wild man that wandered into my map. I reduced his will to 0 but did not enslave him. Was waiting to sell him and thought it might be fun if he dueled one of my slaves. As soon as the slave hit him he went man hunter and all the people gathered for the event ran away and got the lowest quality outcome.
What I expected to happen was for him to fight in a duel like any normal prisoner.
Thanks for the bug report! I was able to reproduce this bug and will get it in for dev review.