horse

What I expected to happen was when i right clicked a tamed horse with a saddle and diamond armor with a diamond horse armor nothing should happen.

What actually happened was it took half of a stack and spat out one so in the end i had 33 diamond horse armor and started with a stack in creative mode.
Describe what happened here

Steps to Reproduce:
1. tame a horse
2. put a saddle and diamond armor on it
3. put more diamond armor on it while holding a stack