Horse spawned on fence with block at +2 Y spawns in the ground

I found out when you spawn a horse on the top of the fence, it can be stuck on the ground.

Here is a list of steps that you can believe me:

Things that you need: 3 glass blocks, 3 fences and a mob spawn egg.

1. The image of the build is down here
2. Spawn a mob on top of the fence
3. Then the mob should be in the ground

 If this bug does not make sense let me know!