Not from a trainer, but from a judge.
I was riding a young horse in one of his first dressage shows, we had done another smaller show, but this one was larger and more than his tiny stallion brain could handle. As long as I kept him forward we were ok, but we did have to halt at X of course. He went straight up. I managed to give him a whack on his ass at which point he jumped forward on his hind legs and literally hopped a couple of times. The rest of the test went surprisingly well.
When I got my scores back the judge had written 'Very impressive, but next time try halting on 4 legs'.