motion builder imports bvh animation wrongly

This is how it imports walk animation

Never seen that before.

Something to try select all of the bones and using rotation set all of the values to 0 0 0. This should snap the rig back into its default pose. Select the root bone and import the BVH into the hierarchy. If it does the same thing then assume that the file is broken and find and try a different walk cycle. (tons out there)