Root Motion Issue

I’ve got an issue when I add a root bone to an animation as I want the anim in UE to have root motion, my issue is not in UE but when Iam updating the anim for root motion when I copy key frames from the animation’s hip to the new root bone, after the copy the whole animation goes weird, I do this in Blender.

Iam posting here in desperation to see if anyone might be able to understand what the issue might be. I’v posted in the blender forums but had no joy upto now so thought I’d try my luck here.

Details of the issue are here