Hitting small horses don't work proberly...

Example:
I was trying to spawn a horse, and accidently spawned a pony... So... I wanted to kill it, but my hits went through it...

What I expected to happen was...:
That i would hit it and kill it.

What actually happened was...:
My hits went through without causing any damage at all. Only a hit didn't miss...

Steps to Reproduce:
1. Get a horse spawnegg (or more than one)
2. Spawn horses untill a pony/small horse is spawned.
3. Try to kill it and notice most of the hits goes through.