Horses that teach lessons on a regular basis deserve a special place in heaven... it is amazing what they put up with! (or I guess some of them don't... :)) I find that attitudes change quite a bit once you make a horse a lesson horse, especially with beginners, and once they get back into a consistent program with you, they change back. Be firm when he tries to do what he wants, rewarding when he's good. Keep reinforcing all of the good things he did before. He'll be back in no time!