Gravity, what's happening?

So I have a 3D robot, rigged with Mixamo.com. Imported fine into Unity 5.3.2 personal.
Animation works fine and the move script works fine. Right now it's just moving him to a way point location and he has a capsule collider, rigid body and use gravity is checked. After reaching the destination and entering a swinging arm animation (Mecanim) he starts rotating as if the motion is reacting as a force against him.
Any ideas on how to fix this?