I don't know anything about BVH files because I've never used them.

But what figure are you using the BVH file on?  Have you tried it on another figure to see if it's the same result?  Are you sure you have IK turned off  for the legs?  Are you applying the pose to the actual body part or a specific part of the body?

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi