The changelog mentions that the decorated pots need to be broken in order to retrieve the items:
Decorated Pots have no GUI, and need to be broken to retrieve or discover their content by players
However, collecting the pot without breaking it will still cause the items to drop.

Steps to Reproduce:

1. Place any amount of items inside of a decorated pot;
2. Collect the pot without breaking it (by not using a tool, using a piston or using a tool with silk touch).

Observed Results:
The items drop.

Expected Results:
The items don't drop.