I believe this is functioning correctly, but there needs to be more research into it. Though the page I cited below does not explicitly say it, there are parameters in place so that players cannot exploit these items. That's the biggest reason they say "House Only." You can put them directly in your backpack, but you cannot put them in a container in your backpack. You also cannot release a secured container in your house that has stone crafted steps and blocks in it.
Housing Craftables
- In an effort to provide more customization options for those players who currently live in towers, keeps, and castles, new craftables are available via the masonry and tinkering skills.
- Walls, steps, and doors can only be placed within a house and have the “House Only” item property.
- There are limits to the maximum elevation these crafted items can be placed. Players found to be exploiting these limits will find themselves subject to GM action if what they build blocks other players housing, vendors, path, etc.
- “House Only” doors can only be placed in non-customizable housing.
- “House Only” walls can be turned via the interior decorator to cycle through available options.
www.uoguide.com