Some NPCs like to ignore the fact that you have rooted them and will still move around while the root is on them. It is mostly the move where enemies walk backwards a few meters in order to make distance and throw something at you or use another ranged attack. For example, I cast talons on an enemy, and the talons come out of the ground and grab them, yet they still walk backwards and the talons slide along the ground with them for a few meters. This happens all the time and is pretty ridiculous.