It's a well known issue in both games. It's the left hand for males and the right hand for females, as I recall. It's particularly bad with the armoured robes Obsidian introduced in TSL.
The generally accepted cause - IIRC - is with the hand helper dummy objects being misaligned, but from memory I checked this once and they seemed OK. It could actually be a problem with the animations themselves, which would mean there would be no practical fix. I guess you could try messing with the position of the hand helpers and see what happens.