Concrete construction ghosts are placed 1 tile out of range of the roboport in the east and south directions.
I can duplicate this bug at will as it happens on every roboport and persists to new save games.
This bug also results in trees being marked for deconstruction 1 tile out of range of the roboport in all directions, however the north and west directions are less out of range than the east and south directions.

To me this sounds like an off-by-one error combined with a slight overlap.

Other than these minor issues the mod works great for me, and doesn't seem to impact my UPS once the concrete laying process is completed.