If you lock the strongbox down and turn it it will revert to the normal weight. You can achieve the bugged 100stone weight by locking down any metal box and turning it (old co-owner boxes will change to 100 stones, or will bug and not be moveable) After you have found one that, when turned, is non-highlightable (is that even a word?) you can use the retrieve function and you will have a 100stone strong box in your pack. People for awhile were trying to sell these on vendors as "server birth strongboxes" for 100s of mils.