Wrong lighting on models adjacent to blocks

Place any model like the cobblestone one I'm showing. Place any block adjacent to it.
If you place an adjacent block in the northern face of your model, all northern faces of the cubes of your model will darken visibly.
If you place an adjacent block in the western face of your model, all western faces of the cubes of your model will darken visibly.
Same happens for east, south, up and down faces