Minecart shooting out of dispenser infinality duplicates Minecarts in certain setup.

When using the setup in the attached picture if you put a Minecart in the right dispenser it will infinality duplicate but not in the left one. I think it only happens if the Minecart is put in via a hopper. I found this out the hard way when it flooded my automatic chicken farm with Minecarts.

Edit: Also it happened when I broke Minecrat with a chest on the track.