My mesh shows what looks like a bogus face normal. The mesh and screen cap show the problem. Some holes still show a face normal but no face can be selected!
I got to this point by creating a building mesh and merging vertices. I created a separate mesh (plane) for cutting holes in the building. I used knife project to put cut lines into the building. Then I selected and removed faces where holes should be. Some holes still show a face normal even though there is a hole (no face can be selected). Merging vertices does nothing.
This appears to be a problem, but I don't know if it causes anything bad.