Put the summary of the bug you're having here:
After taming a horse and saddling it, I decided to put some armor on it. To my dismay, my trusty steed turned invisible. All that was left was it's shadow moving around on the ground.

What I expected to happen was...:
I expected to just put the armor on the horse.

What actually happened was...:
It became invisible.

Steps to Reproduce:
1. Tame any wild horse (mine was naturally spawned, idk if an egg spawn would act differently)
2. Saddling works just fine.
3. Put on armor of your choice. I started with diamond and worked my way down. All of the armor made the horse become invisible.
Note: You can remove the armor, ride the horse, and access it's inventory still.