When killing a leashed mob while on a horse causes the leash to disappear and not drop

When I had an animal on a lead and started to ride a horse I accidently killed the animal with my sword and the lead that was attached to it did not drop.

What I expected to happen was...:
I expected the lead to drop when the animal died

What actually happened was...:
The lead did not drop

Steps to Reproduce:
1. Attach a lead to any animal
2. Get on a tamed horse
3. Kill the animal that is attached to the lead