Could that be scale animation keys for certain bones (or
group of bones)? In case there is a single skeleton file for all clothes/armor
(like in Oblivion) manipulation of this skeleton might affect shapes of all in
game meshes for the race or in the best case scenario particular character, PC
or NPC. I guess something like that is realized in Morrowind where it is
possible to change race height/weight once with two clicks in the editor without
working on a mesh level for every cloth/armor.