Animals/Horses break lead after restart + loading chunks

Currently i was making an adventure map and I needed a couple horses tied to some fences but after restarting the game, I noticed that at random occasions (not every time), the lead would break. Although It only occurred when I restarted the game a couple chunks away from the horses, never when I was nearby. This makes me think it has something to do with the chunks loading after restart.

The pictures below shows at two different times what happens after I restart the game, the lead appears to break and drop onto the ground. its very frustrating because i'm trying to get these horses to stay but no matter what I do they always escape.