Whenever you call entity.remove() on a LeashHitch entity, a lead item is dropped at the entity's location.

I'm not sure if this is expected behavior, but when we do the same on a painting or an item frame, they do not drop anything.

entity.remove() should simply remove the entity without spawning any item.

I made a small plugin to test this out.
You can follow these steps:
1. attach lead to any entity
2. attach it to a fence
3. in survival mode, break the attached leash
4. a diamond and a lead will drop

another testing:

1. attach lead to any entity
2. attach it to a fence

3. right click on the leash with an empty hand

4. send a message in chat
5. the leash is broken and there's a new lead on the ground