I have a rig that has motion capture on it. It filtered and looks ok but some of the limbs need repositioning.

I create a new layer and set a zero key before and after the bit that needs changing.
I move to the frame to edit and move the effector to the correct location.
I hit key, and the limb leaps to a new location.
Move it back, and hit key, and again it leaps.

Every time I set a key it causes the limb to jump around.

This also happens with autokey. Move an effector and release to watch it jump.

Incidently the move appears to be roughly double the distance I move it, as if its adding it twice. In the fcurve editor you can see it jump for every key attempt.

The additional layer is default and set to body parts, additive. Base is locked.

Does anyone know whats causing this?

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3DS Max Entertainment Creation Suite Subscription, BonesPro, FumeFX, Flatiron, Unity3d Pro
Windows 7 x64, 16GB, Quadro FX3800
Windows 7 x64, 12GB, GeForce GTX580