Strange Character Movement (Mecanim)

Hello, I have a humanoid character that I have animated with Unity's Mecanim System, and there have been some problems. I currently have a walk animation that is set to play when a "Speed" float reaches a certain value, and is controlled by another script. When the "Walk" animation is played, he hops backward (the character itself moves backwards) a small bit on the first loop, then hops forward (goes back to normal position) when the button is released. I checked the animation in Blender and this movement doesn't happen, and the problem isn't there when we run the animation using the Legacy system. I can confirm that the transform is not changing either, so I believe it is a Mecanim problem.

Any help would be appreciated!