Lead remains attached to the fence when the mob is killed

The bug

Lead remains attached to the fence when the mob is killed.

Steps to Reproduce:

• Place down a fence and obtain a lead.
• Summon a pig and use the lead to leash it to the fence.
• Kill the pig and watch the leash knot closely.

Observed Behavior:
Leash knots remain attached to fences when the leashed entity is killed.

Expected Behavior:
Leash knots would not remain attached to fences when the leashed entity is killed. Instead, as soon as the leashed entity is slain, the leash knot should be destroyed.

Code analysis

Code analysis by [Mod] Chandler can be found in this comment.