I had my horse inside of my house and I mounted it undera double door way. There was also a spot that was two blocks tall missing from the wall next to me and the horse and when I mounted the horse the game instantly crashed. When I reloaded the game I was in my spawn location holding no items and with no xp. I assumed it had killed me.
I was playing on the xbox one on survival.

Steps to recreate:

1. build an area 3 blocks tall with horse inside with both armor and saddle.
2. have horse under a double door way (or possibly just a two block tall location), very close to a wall with two blocks cut out.
3. Mount the horse.