Bug occurs In both Creative and Survival, with default appearance or an added Resource pack.

Dark lighting under overhangs is not yet fixed when the overhang is only one slab's height above the surface on which the shadow falls.

Attached screenshot 2013-10-24_11.05.jpg shows an overhang from a pitched roof created by stepping slabs.

Attached screenshot 2013-10-24_11.21.jpg shows the problem reduced to a simple structure.

Attached screenshot 2013-10-24_11.22.jpg shows the simple structure with a full block's height between the overhang and the underlying surface.