When the mobs wear the lead and the lead is attached, it doesn't appear on the block and I can't take it of. Also if the block is destroyed, after a few moments it drops under the mob.

What I expected to happen was...
The lead should be on the block and it would drop if block was gone

What actually happened was...
It disappeared and after the block is destroyed, it drops under the mob.

Steps to Reproduce:
1. Spawn a mob, like a horse (a mob what you can hold with the lead)
2. Attach the lead to the mob and to the fence.
3. Destroy the fence.