Resolution: Works As Intended
Before Snapshot 13w21a, I had several horse armors, both iron and gold, in a stack. I removed one from the stack to try the new feature with horses, but when I went to go put it back in the stack, it will not stack. I test this with the iron and gold armor.
I just tested in creative with the same results.
- relates to
MC-13801 Horse Armor Stacks