The bug

If a composter is filled with at least six levels of compost, and a trapdoor is placed above it, players that are inside of the composter cannot open the trapdoor and thus cannot leave the composter without destroying it.

This issue also happens with at least four levels of compost, but then it is still possible to open the trapdoor by jumping inside of the composter.

To reproduce

1. Place a composter
2. Right-click onto it with six pumpkin pies
3. Place a trapdoor on top of it
4. Jump into the composter
5. Close the trapdoor
   → You're now trapped inside of the composter and cannot escape it without destroying it.