I copied/pasted my answer from HGS :)
Just to put it here, too, since there may be different people looking....
A correct lead change is from back to front. It is hard to tell from your video... your horse only hops for one of the changes. It really looks to me like he is just trying to do a correct lead change, but it's harder since he is going so slow. Can you get a video of you riding more forward? A nice working trot, canter, and lead changes?
I really feel like he is just putting a little "oomph" in there for the change. Has he been evaluated for soreness and saddle fit? Another thing could be that he is slightly protesting the use of the spur... but I don't know, since you are using them other times without a fuss.