Falling Sheep

When I flew out of the chunk and went back, there was a jeb_ sheep that I had leashed that was flying, attached to the leash. When I was in the chunk, it was on a 1 block thick floor of oak wood. To reproduce:
1. Spawn a jeb_ sheep on a platform 4x7 of oak wood 26 blocks from the ground.
2. Put fences around the edge
3. Leash the sheep on the left corner fence
4. Fly away from the chunk and come back
(PS These steps do not always work)