I know a gelding that has been in the owners possesion for two years. Came off the track as a 5 year old, sound, but needed some time off from hard work because of an over stressed tendon in a hind leg(dont know specifics.)
-the first 12 months he was well behaved. Had some down time, did a bit in the arena, lots of trails, went to the mountains. Had some get up and go but generaly quiet. Had to learn typical ottb things, steering, reverse, etc.
-next six months got a bit zippier, the odd crow hop, some prancing. Kept the rides w/t/c very little fast work. Attributed it to his tendon issue being completely resolved and feeling great.
-Last 6 months. Not ridden a ton, but has become a big handful. If you try to walk him for a ride, he spends the whole thing tossing his head(same bit, teeth done, same saddle), bouncing around, prancing, crow hopping and generaly being an butt. He even pulled back and broke a halter, which he did not even hint at doing for the first 1.5 years. Do you think its all behavioral? Or is their some sort of deficency that could cause it?