Moss Carpet does not appear on the map when placed on stone brick walls

On the smallest map scale, mossy carpet does not appear on the map when placed on top of stone brick wall, glass, or some other materials (see attached screenshot).

For context, my base consists of a giant platform of stone brick wall at elevation y=64, with mossy carpet covering the whole thing. On the map, it should appear green, but instead reflects the stone color of the brick wall beneath the moss.