Obviously, no one is STEALING from these barrels, they RESPAWNING, turning all the stuff you stashed in them into 4 Apples, or whatever relatively worthless item was originally in there. This brings up another advantage of home ownership in the game. The trunks & cabinets & lockers & safes in your house don't respawn, but the miscellaneous items that your house was originally decorated with DO. So, grab that bowl full of pearls, and take all the alchemy ingredients laying around decoratively. THEY'LL BE BACK!!!