Horses eat underwater

What I expected to happen was...:
To lead the horse out of water.

What actually happened was...:
When leading the horse out of water, it decided to sink to the bottem and eat some dirt/sand.

Steps to Reproduce:
1. Tame and equip a horse with a saddle and diamond armor. ( I did it )
2. Lead it into a 2+ block lake or ocean.
3. It may eat in the bottem of the ocean/lake.