horses break lead when being lead when they stop to eat grass

What I expected to happen was...:
The horse would continue to follow me until I unleashed it or tied it up

What actually happened was...:
breaks lead while being lead when it stops to eat grass

Steps to Reproduce:
1. put tamed horse on leash
2. walk, sprint, ride on another horse
3.after a while the lead horse will break off lead as it eats grass