There's also a clear contradiction in the explanation at the end. It's established that covering something in black makes it invisible but still has mass (ex. the footprints left by Darklaw). I find it hard to believe that in 10 years not a single townsperson accidentally bumped into the huge bell tower hidden in the middle of the town square 😛 Even if the Shades ring their bell and turn the townsperson around if they get too close, surely someone would realize there's a huge patch of ground that nobody is able to walk on.
I suppose the townsfolk could all just be super obedient towards "Keep Off The Grass" signs?