It's imported wrong, I guess. There was a program called Mender (search WEB for it, it was a free tool from The Game Creatiors, if you won't find it, PM me), it used to fix some animation issues in those .x models. Also, I wouldn't import them streight into the MED, but would use FragMOTION or MilkShape instead (but those aren't free unfortunetly). Maybe blender could be used to import those models into the MED, give it a try!

Greets!