Bug: as soon as the building was started, the “doodads” (doors, windows, lamps) appeared without having been crafted or placed before (i.e. the crafter had never even made any of them)
I closed it before realising I should take a screenshot, but this picture was in the save folder:
As you can see, the doors / windows should not be there.
It may help you to know that this bug also occurred after I reloaded this world.