This is not a bug actually. Issue here is that your are pushing normals way out of the 'safe area', making many of them reversed compared to default ones (computed from neighbor face normals).

Up till 2.76, Blender did not handle correctly that 'inversion of normals', leaving *face* normals opposed to its vertices ones, which was really bad and inconsistent. Since 2.77, winding of such faces is now reversed, to make face normal match the direction of its vertices ones.

In your example .blend, several faces are 'reversed' that way, producing the black patches. I’ll commit soon a new setting to the modifier allowing to limit the maximum angle between original and new normals, keeping this below 90° should help prevent most of those face normals inversions.

Editing normals in such an aggressive way also raises another issue, present since the beginning, which is it makes the terminator problem much more visible. Nothing to be done here really, you have to handle it yourself I’m afraid.