Patty probably chopped the legs off tables, and raised them prior to placing the boxes below. It is a use of a bug that the devs have winked at, long used by psychotic UO decorators (not that we have any of those around). There is a
detailed tutorial on the Homes & Castles forum - you can modify the technique to many applications.
You can do some amazing things with the chopped add on, and goza stacking technique.
-Skylark