If you break a decorated pot in a "hall" room of a trial chamber it wouldn't stack with normal decorated pots in your inventory.

Steps to reproduce:

1. Create a new world with update 1.21 experiment enabled
2. Set your gamemode to survival mode and difficulty to peaceful.
3. Give yourself less than a stack of decorated pots
4. Locate a trial chamber "hall" room
5. Break decorated pots found in that room.
6. Notice that broken pots don't stack with normal decorated pots in your inventory