What I expected to happen was...:
When i had a sheep tied to a lead and flew into the air the lead would snap and the sheep would fall to its death

What actually happened was...:
i flew into the air and the lead did not snap so i manually removed it from the sheep the sheep then kept flying as though still attached to me via an invisible lead. The sheep did not die until i landed back on the ground. This does not occur with pigs haven't tested cows or other mobs. after a few attempts on this the bug stopped but maybe you should still check out

Steps to Reproduce:
1. connect a sheep to lead while in creative mode
2. fly into the air
3.release sheep from lead it should continue to fly