Bizarre indeed! I wonder if maybe he is picking both fronts up as if to go into a canter or something. If he was trotting like his legs suggest, it seems weird to me that he would be picking up the left front if the right is so out of shape. I kind of wish that I could see the what the right rear foot was doing!

And I think I've just spent way too much time puzzling over this, lol

Oh yes, maybe - although his hind legs etc. don't seem to be engaged for canter! Haha! Maybe he's just a weird horse. :P And don't worry: time spent puzzling over a horse - particularly a heavy horse - is time well spent.