PHAT Stretching When Simulating With A Bone Selected

I am using a rigged asset I got from opengameart, (Pony | OpenGameArt.org) and exporting it to FBX with blender, importing it with its animation and trying out the PHAT stuff. I cannot seem to figure out why I am having massive stretching issues while simulating with a specific bone selected. It always seems to be two bones that are attached to each other that stretch if they have some kind of physics applied to them.

Here is a video demonstrating whats going on.