I don't know if this is supposed to happen, but when a lead is tied to a fence and I right- click it to take it off, it turns into an item. It seems like you would pick it up again, but it falls to the ground as an item. This happens for both the wood fence and the nether brick fence. Also when you right-click an animal a second time to get the lead off, it falls to the ground as an item. This applies to all animals.