Win10 x64 / GTX 780 latest nVidia driver
Broken: latest builds from buildbot
Worked: official 2.78b
Short description of error
The viewport shows correctly smoothed normals (e.g. when setting an object to "smooth" and activating "Auto Smooth" at default settings), Cycles renders them as hard.
I noticed that Sergey made some commits where he mentioned split normals on wednesday 15th that might be the cause.
BTW if I deactivate "Auto Smooth" but keep the object "Smooth" both versions of Blender give the same result.
Here the correct result when hitting F12 in an official build (2.78b in this case):
And here the result with a current build from buildbot:
Exact steps for others to reproduce the error
Load the attached blend file and press F12.