Reported by players on my server. Leads are duplicating when used to lead a horse through a teleporter. We've haven't tired other animals yet.

Lead a horse into a teleporter. Teleport completes, horse is still on lead with you at the receiver pad. However, if you go back to the sender pad, you'll now find a lead on the ground.

(most of my players don't use horses, so it's not surprising we're just now discovering this)