It's easy to break the AI in the game, to a point of being ridiculous. Since all the enemies are on a tether, once you figure where that tether is...
For example, melees ai is simple-Avoid grenade areas, get target. When you apply the tether, it becomes-
1-Avoid grenade areas
2-mind the tether area
3-Go to tether if possible
So what happens if you put a grenade between them and their tether? They freeze up. They try to retreat to the tether area but can't, and they can't cross the grenade, so they'll just sit there.
http://a.pomf.se/tpjsiv.webm
Harmless. Ranged enemies will shoot at you when possible, otherwise melee is a bit broken.