When Wyll and Tav nearly kill a zombie their on kill abilities seem to trigger before the zombie is reduced to 0HP. I haven't noticed whether there is a another reason the zombie might die anyway. I first noticed this on the Tav with the fancy cloak, after the unfortunate incident, and now again and with Wyll getting Dark One's Blessing in another zombie fight, when the zombies was on 1HP

I think that is not quite correct.