In your Parameters Tab, select Show Hidden, then select the model and type jcm in the search box. You'll see dozens of jcm's - scroll down and find one that is way out of whack (like 500% or something). It will probably be labeled left thigh or something like that. Just zero it and try the movement again, then save the DUF with that jcm corrected.
It happens when another morph was used at some point in the past and that jcm then gets saved like that. We call those rogue morphs and they can be a PITA.