Adding a bowl of pestled herbs to raw soap that's in the world (on a counter or the floor) makes the whole bowl invisible, the bowl spawns again later in the inventory.

reproduction steps

1. Drop a partition pan with raw soap in it on the floor
2. Drag bowl with herbs to the raw soap (Tested with a critter with medicine Skill), you'll lose the whole bowl.
3. Wait for an unknown period of time, the bowl with the herbs will re-spawn.

Edit: testing with a cup of water deleted the bowl too, but I still didn't get the bowl back