Normal Map + Micro Displacement = Bug? In experimental render mode I tried to combine micro displacement and normal map. This has been a common workflow for high Quality materials in other 3D applications.

While I can render normal map in supported mode:



in experimental mode it turns object very dark (this is not the issue of object/tangent space, you still can see object little bit)



not much changes when I add displacement

turning normal map off, the objects reappears with displacement, I miss the fine detail of normal map however



Small remedy is that you can plug bump map into normal shader node, this adds the finer detail, I find bump maps much inferior to normal maps however. 



I have reproduced this bug with other normal maps too. I have double checked that normals are set to non-colour data. Is this well known and reported bug, or am I missing something else?

Thanks a lot in advance.
File:
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It seems as of version 2.79, displacement node, Adaptive subdivision (experimental mode) cannot be combined with normal map node. Workaround for now is either using only bump map or switching off the adaptive option inside of subdivision modifier. 

This bug is not noticeable when using simple plane: (probably here tangent space is same as object space)


In case of a sphere, shading artefacts appear when combining Normal Map and Adaptive Displacement


Unfortunately I now have the file in version 2.8 only
http://gofile.me/2mjhf/tn9buuTmU

Node setup in 2.8:


Correct me if I am wrong, but it seems like developers were aware of this bug and changed it in the upcoming version 2.8. Since that is around the corner I can live with the 2 above mentioned workaround in 2.79 until then.

Thanks