So I brought him in and groomed him and put the side reins on. I took him out to the arena and stopped to shut the gate. When I asked him to move again he gave a small rear. I turned to look at him and suggested he get over himself. He started to back up. I released all pressure. He was about 5 feet away from me when he decided to start trotting and then cantering around the arena. I shut the arena door and went to a corner to watch.
And there were fireworks to watch. I believe what I witnessed was a tantrum. He cantered and bucked and straight-legged bronced, and did all manner of hysterics. I let it run its course. It actually took about 5 minutes which is a pretty long time.
When he stopped, I went up to him and petted him and attached the lunge line and put him to his usual work. He eventually came around to lovely politeness.