I think that there was a similar report some time ago and we came to a conclusion that this is expected, and also happens in other renderers.
What you could however try is:
-adding a "smooth" modifier (not turbosmooth or mesh smooth - just "smooth") and making sure that there are no separate smoothing groups (that the whole object is smooth)
-in "advanced options" of the material, you can try changing anisotropy from local axis to uvw
Can you share a sample scene with this issue visible?