Riding on a horse leashed to a block high in the air causes the horse to fall as if there was no leash

Heres what I expected to happen:
1) Leashing the horse to a really high block will cause the horse to float in the air
2) Riding the horse will make you sit on top of a floating horse

Heres what really happened:
1) Leashed horse the the fence. He kept bobbing up and down
2) Riding the horse hoping that the same will happen to me - The horse fell onto the ground and died as soon as I rid it.