Cycles - Material problem. Small black stripes over surface where thre must be none

I have strange problem in Blender 2.72 - instead of some edges i have small black stripes on surface where there must not be. I do not use noise texture in this material.
Here is rendered material

At first i thought it is problem with wrong direction of normals.
I checked normals and they looks correct

Then i apply the same material to default cube with four level of subsurf and result just the same - black stripes instead of some edges.

What can possibly go wrong? How do i fix it?

Here is material nodes

1 Like

Thank you! I thought it is some serious problem with materials, or something like that. If this is just a simple viewport bug which does not affect final render, i will not care about it.