a horse in a nearby corral was duplicated about 64 times.

At that time I was using a powered rail glitch duplicator and made about that amount of powered rails. This happened twice.

I don't know how/why the horse duplicated,

I don't know for certain if there's an actual relationship between my redstone glitch duplicator

Steps to Reproduce:
1. Duplicate N powered rails
2. ...see very crowded corral with about N identical horses
3. ...