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.
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Sorry I thought this was different because it doesn't just increase the amount. Only one is ever in the dispenser but it keeps shooting out.
Duplicate of MC-5998 , please use the search function to see if your bug has already been submitted. Currently over 40% of tickets are being closed as duplicate.