Walking under jad would complicate the situation a lot since it would have to account for his movement, but it walks into melee range so that it can reach the healers and get their attention to prevent healing, then it must stay close to prevent the healers from losing aggro; Did it not attack healers at all?
It should attack them to get their attention, but not kill them; Does it not walk into jad's melee range to attack healers right after they spawn?
They should be quite fast, have you selected the hardware mouse?