But it looks like you don't really become the horse. More like the game forgets to put your character model on top of it.
I don't know - from the ending, it looks like the game is still rendering land based on where the actual character model was left. It shouldn't do that if it just forgot to render the character model on top of the horse.
Cool and random find though John Ryan. What control options do you have? Can you shout / cast spells / use "mounted" combat?