Horses - Killed With Nether Portal

Horses die entering the Nether.

I expected horses to go into the nether while riding a minecart.
I thought the horse would go through.

What happened, well they took damage and died.

Steps to Reproduce:
1. I spawned a horse.
2. I put him in a minecart connecting to the nether portal.
3. I then pushed the minecart into the portal.