Normals are fine. Mesh is triangulated. Surface is flat.
(these are the most common answers to that problem, but not in my case)
You can see it at the screenshot below.
Picture: object mode above, edit mode below.
You can see that the inner (smaller) cylinders have less faces, and the outer cylinder (larger) has twice as much (I did subdivide it). I can assume it is relaed to that subdivision. I have made subdivision (selecter upper and lower edge of cylinder and pressed W - Subdivision), then selected new edges and scaled them on X and Y axis on 1.05 (or on some similar multiplier).
What can this problem be caused by?