Automatic Composting isn't consistent

When I place a bunch of Warped Wart blocks into a system to get automatically composted, the result is not Bonemeal but instead the Warped Wart block. This does not happen often but it does happen.

Steps to reproduce: 

1: Have a Hopper above and below the Composter to automatically convert and harvest

2: Load compostable items and wait

3: Check the Chest/Barrel to see if the bug occured