Duplication of entity in minecart

I had a villager in a minecart moving around in a circle for a lighthouse built by this design: https://www.youtube.com/watch?v=wvoJqX6M1uI

I noticed that the lights were a bit off a few days ago (possibly before 1.8.2), but I didn't check on it. Today, I went up to turn it off and their were two carts with identical villagers.