Cheetah3d - Random rotation At Keyframes

My first animation...

I was wondering if anyone else has seen and weird popping in their animations. I'm using Cheetah3d (where it animates correctly) and have tried exporting to both FBX and JAS file types. My model is a humanoid made out of simple primitives and I'm only trying to animate the legs at the moment. Here is the hierachy in Cheetah:

Leg (folder)
-Hip (primitive)
-UpperLeg (primitive)
-Knee (folder)
--KneeJoint (primitive)
--LowerLeg (primitive)
--Ankle (folder)
---Front Foot (primitive)
---Back Foot (primitive)

When it is animated in Unity it appears to be randomly rotating the knee and ankle at each of the key frames. It is a quick pop in the animation before resuming normally before hitting another frame.

Do any Cheetah/Unity users see where a problem could come in? Is it because I am using folders and should recreate the model without them?

Thanks

 

Does anyone use folders when making their models in Cheetah3d?

Thanks

 

Here's the files.