Leads Disappear after killing the leaded mob

Put the summary of the bug you're having here

What I expected to happen was...:
After killing a "leaded" (correct term?) mob, (chicken) I thought that the lead would drop as an item or stay in my hotbar.

What actually happened was...:
After killing the "leaded" mob the lead disappeared.

Steps to Reproduce:
1. Spawn chicken from a spawn egg.
2. Lead the chicken.
3. Kill the chicken while it is still on the lead, using a diamond sword.