I have a barrel in my hands. I can drag items from my inventory to the barrel, and from the barrel back to the inventory. The items appear (visually) similar to "attachments" on the barrel. I can also "View Contents" on the barrel. The barrel is permanently stuck open, and cannot be closed.
I have not been able to drop the barrel, even after logging out and back in. Throwing it does not work. I can climb ladders with it. I can't pick apples.
I'm not sure how it happened. Possibly I drank a canteen while the barrel was in my hands.
Here is a link to a video demo: