OKay been fiddling with this for the last 24 hours and I've gone batty over it. The foot on the Z and Y rotations drags the upper shin on the left foot.

Things I've checked.

1. Joint Setup: Mirrored from right foot, problems don't exist there. Used FallOff zones to exclude the upper shin, no difference. Moved joint center around as well as the extents of the bend, very little difference.
2. Groups: I've regrouped and imported the obj multiple times with "Make Polygon Normals" and "Weld Vertices" enabled. Attached below are screen shots of the offensive area's groupings.

Any ideas, or people willing to take a look at it? This was going to be a sale item when completed....

(Attachment 1: The broken shin)