Three solutions for this, as I see:
1st solution: Download a backup of the skin that's bugging, and replacing. It seems to be a bugged bone in the skin.
2nd solution: Download a backup of ped.ifp, it maybe be changing the stances, therefore the bones also move, so it may bug that one.
3rd solution: Try rebuilding the file, instead of just saving him.
In case you don't know what's a bone, it's a part that is inside the skin, that is like his skeleton, if there is a bugged bone, your skin will be bugged.