fighting having rear leg picked up

Over the last 3 weeks, my horse pulls his right rear leg from me when I am cleaning his hooves. The farrier was out yesterday and could find nothing wrong with the hoof. So we both thought that maybe, since it is cold and he has been inside a lot, that it could be a stiff joint issue. He only does this when his right rear is picked up. I can stretch it out behind him and forward. The higher it is picked up, the more he fights and hops.
He is going into the vet on Monday for shots and check up, so I will be talking to the vet about it.
Between myself, farrier and a friend, we cannot decide if it is : 1. A balancing act issue when he is standing on his left leg, 2. Stifle stiffness in either leg needing some excersize, or 3. Soreness in his right hip.
The farrier and I think it is more a balancing issue with a little stiffness in the stifle. He will stretch that leg out as long as it is not picked up too high. Friend at work thinks it is soreness/tight ligament in the stifle from cold and not enough excersize.
He does not have a noticable limp or any other signs of lameness.
Inconclusion: I am bored and thought I would ramble on a little bit to see if anyone here might have experienced anything similar.

Sounds like you have drawn the same conclusions I would have. The only horse I've had a huge problem with picking up a leg was a horse that had some pretty major stifle issues. It sounds like you're on the right track to getting it fixed, or at least having a diagnosis :)

Have your vet show you some stretching exercises for your horse. When it's miserable out, Sun stays in his 'house' and gets stiff. Doing some stretches on his legs, esp. The rears, really helps keep him limber!
Just in case, have the vet do a hoof test to rule out abcsess!