Lead remains attached to the fence when the mob is killed

No, this is a different issue. That one refers to a player death, this one refers to the death of the leashed mob.

Still present in 1.8.

can confirm in 15w45a

Still an issue in 16w33a

Confirmed for 1.13.1.

Confirmed for 1.13.2-pre2.

@MisterSanderson, 1.8 bugs are not accepted anymore. 1.13.1 and 1.13.2pre2 and (FUTURE UPDATE) 1.14 bugs are accepted

in 1.15 pre 6

Confirmed in 20w20b

Confirmed in 1.16 Pre-release 2.

Confirmed in 1.16-pre3.

Confirmed in 1.16-pre4.

Confirmed in 1.16-pre5.

Confirmed in 1.16-pre6.

Confirmed in 1.16-pre7.

Confirmed in 1.16.3

Can confirm in 20w51a.

Can confirm in 21w03a.

Can confirm in 21w05b.

Based on yarn 21w05b mappings: at net.minecraft.entity.mob.MobEntity.detachLeash() the leash is removed, however no check is in place for the leash knot:

public void detachLeash(boolean sendPacket, boolean dropItem) {
        if (this.holdingEntity != null) {
            this.holdingEntity = null;
            this.leashTag = null;
            if (!this.world.isClient && dropItem) {
                this.dropItem(Items.LEAD);
            }
            if (!this.world.isClient && sendPacket && this.world instanceof ServerWorld) {
                ((ServerWorld)this.world).getChunkManager().sendToOtherNearbyPlayers(this, new EntityAttachS2CPacket(this, null));
            }
        }
    }

Fixing it might be as simple as adding the following near the top of the function:

if (holdingEntity instanceof LeashKnotEntity) {
          this.holdingEntity.remove();
}

Can confirm in 21w06a.

Can confirm in 21w07a. Video attached.

Can confirm in 21w11a.

Can confirm in 21w14a.

Can confirm in 21w15a.

Can confirm in 21w17a.

Can confirm in 1.17.

Can confirm this behavior in 21w39a. Here are some extra details regarding this problem.

The Bug:

Leash knots remain attached to fences when the leashed entity 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.