Agropelter vanishes

I was hunting an agropelter. I bullrunned it for laughs, and it then took about 3 steps towards a tree, and despawned. It wasn't penned in or anything, and there were plenty of trees for it to go into.
EDIT: it's flock did not despawn. However, out of the 2 agropelters left, I killed one, and the other one despawned while it was going to a tree. I think the cliffs in this area confuse their AI or something.
EDIT: it's flock did not despawn. However, out of the 2 agropelters left, I killed one, and the other one despawned while it was going to a tree. I think the cliffs in this area confuse their AI or something.