I've been working on collection with him, but I haven't been harsh on his mouth as to make him that way....at least I don't think I've been. I'll milk his reins (gently moving on then the other) and he'll collect himself...then I'll give him a loose rein, but the second he looses the collection, I milk the reins again.
Yesterday during lessons we were working on transitions. Going from a walk, to a sit trot, to a canter, then to a post trot, then to a sit trot, then to a stop. All went alright, but the minute I asked for a canter, Sonny sped up into an extended trot (he didn't canter) and as I tried to slow him down he'd extend his head and wouldn't slow down. I had to turn him in two really tight circles, then lead him into a wall for him to stop (we didn't hit the wall, but he sure came close).
The reason though I think it's an attitude is that he's TOTALLY sensitive when I ask him to back up or to leg yield. I'll just put a little pressure and he'll side-step or back up.
I think he's just being a brat....but what do you all think?