I've seen this in 7 with sr1 and sr2. Namely hair wigs (or anything that is a prop attached to the head) see to get their geometry shifted around and not from poses. Its as though the actual origin of the hair gets moved so that a position of 0,0,0 becomes some other numbers but the wig stays still. Then, after some moving it will shift around. I have double checked to make sure this isn't just some pose that effects hair. For example I also have masks on characters and earings and they move around too. I also made sure they are children of the head and not of some clothing head.