Thank you all very much )
Mar 24 2017
Mar 22 2017
The issue is coming from hardcoded MAX_SOCKET set to 64. I've tried to remove such a static limit, but it's not so trivial within the current nodes design, especially for the texture nodes. I think it is safe to bump this constant to 512. This will only be ~16K extra stack memory usage per thread during evaluation which is really small for the modern systems.
I also have struggled with this kind of artifacts and found a simple trick how to avoid them. Basically you can calculate a dot product between normal and incoming vector and attenuate the normal map where it could cause problems viz https://blenderartists.org/forum/showthread.php?382497-Black-material-artifacts-on-flat-angle-surface-areas
I can reproduce the issue with 2.78b, but not with 2.78c and master.
Please try updating to 2.78c and checking if it also fixes the issue for you.
Mar 21 2017
Mar 20 2017
Feb 14 2017
Nov 2 2016
Sep 17 2016
the nvidia shader compiler is not having happy thoughts about this monster of a shader and calls it quits