While we're here ... I set roof:levels to 0 for one of these buildings. The description for that tag says "Number of floors within the roof, which are not already counted in building:levels=*." The house in question has a pitched roof but no floor inside it (there's an attic but it has e.g. no floorboards, no windows, and no access other than by a ladder). Should the value be 0 (as I set it to) or 1 (as you changed it to)? It's not obvious to me.

Hmm. If I follow the link from the "building" tag, the page I get describes the value "detached" as meaning "A single dwelling unit inhabited by family or small group sharing facilities such as a kitchen." and "house" as something _less_ specific than that. Are you really sure "detached" isn't right?

Might be worth taking that up with the makers of the StreetComplete app, which gave me a menu of options from which I selected "Detached house". If they're sending something less specific than that, it's likely a bug. I'll double-check what I'm doing and take a look at their code...