Lighting of parallax mapped object seems to be inverted when using directional light.
playground: http://playground.babylonjs.com/#1SGTPA#5
The scene contains paralax mapped rectagle and few spheres, the only light on the scene is directional light with the direction equal to (0,-1,0)
The mirror is not so important here.
When looking from the side of spheres, light on the plane goes from down, on spheres it goes from the top
but when we rotate the camera and look on the back face of plane, suddenly light there goes from the top
same example, but light direction changed to (1,-1,0): http://playground.babylonjs.com/#1SGTPA#6