I placed a pre-fab Shared Sleeping Quarters in my town. After it was finished, the workers had erected a ladder to place a lantern on the wall, but never placed the lantern.
I manually placed a lantern at the spot where it was supposed to go. Suddenly, the ghosts of ladders sprung up all around my building. Then my workers proceeded to build up the ladders and fill in scaffolding between them. It’s been a little while in gameplay now and it’s still all there.
The building is still functional as sleeping quarters for new hearthlings. It’s just weird.