When entering the trial chambers, there are the newly decorated pots with their inventories. Since inventories are generated upon opening them you can place items within the pots since they are counted as empty until the loot is loaded. If you place an item in the pot such as a sword or anything else, then break the pot to get it back, you will only be rewarded with the intended loot pool, losing the inserted item. I can assume this is a known issue, but this is my assumption of what causes this bug in particular.