Is this a known glitch?

@Simmingal I found a temporary work around, if you flatten terrain to height you can add the tiles without that but, you have to move 1 full grid square in from the edge of the lot, if you try to add them so that they butt up against the unbuildable sidewalk area they do that lifting thing. The lot starting from the second full grid square in sits below the level of the sidewalk.