When a companion decided to attack an enemy, it "locks" it out of player auto aim.
For instance, if a biter is running towards me and I try to shoot it with my machine gun using auto aim (just hold space), this entity is not targetable if a companion decided to attack it, and since the "laser rockets" take time to reach and ultimately kill that biter, I can't shoot it in the meantime, leading to the biter reaching me and attacking me. This isn't too annoying when the companion targets a nest, but when the target is an angry biter coming at me and I can't even shoot it, that becomes a problem.