I can only tell you what happened to me. I have done this a few times.
I own the watchtower hall (crafted castle). I bought the new aquariums to hold my fish that I catch. I wanted to place the tanks in the bottom of my open tower, the one in the back with the open steps. I have a few items on the top floor. the items that I had trouble with are the: PLAYABLE PIANO WINTER BED LAMP POST
OK, so I placed the following tanks on the bottom floor of the tower under the items. Regular Keeper aquarium, Regular Small fry aquarium, Tall keeper
When I removed the tanks the items on the above floors also went back into my backpack. ad they went like this: Regular Keeper aquarium, - PLAYABLE PIANO Regular Small fry aquarium, - WINTER BED Tall keeper - LAMP POST. I did this a few times. And each time I had the same result. It only happens when the tanks are placed in the floor of the tower,( under the items) I did this in another location in the castle and it was fine.
I hope this helps the Kingsisle team.
Mark Dragonleaf L89 Storm
PS if you want more info via email, please let me know.