OK, I entered a duel with a death knight for the last hour, and see what you mean. Target order was slightly off. I've fixed it, and it prioritizes human players first over all others in all cases. In dungeons and PVE playing, this should have zero impact - but in battlegrounds and duels, it has a lot of impact! I hope I didn't introduce another bug by fixing this bug, but let me know - I was too tired to test it in battlegrounds by the time I was done.
It also prioritizes kill weights by class. Anything that could be a healer will be killed first, general casters are killed next, anything that is melee is killed last. These are preferred above other targets, even ones attacking your healer, even ones you currently have targeted. That's where there might be a bug.
Let me know!