Cycles SSS not working on AMD Radeon GPU From my google fu I leanred that SSS has been implemented on GPU for Cycles since 2.72 in the experimental kernel.  I'm on 2.78b and I'm just getting a black shader like when it doesn't work.  I installed 2.78c, and it's still not working.  Any guesses as to what setting may be borking me here?  Any ideas where I should focus my troubleshooting?

Blender 2.78c
OS:  Windows 10 64bit
GPU: AMD Radeon R9 390
CPU: Intel i5-6500 3.2 GHz

P.S. I can't create an SSS tag for this post till I have 300 reputation.  If anyone else agrees with me that SSS would be a good tag and has 300 reputation, feel free to tag it :)
The fact that a feature is supported in Cycles doesn't mean it is supported for all computing methods, nor across all devices.

It is largely known that OpenCl computing on AMD branded cards is not at the same level of support as CPU rendering or CUDA on Nvidia cards. Not only is performance non-optimal, there a lots of bugs and limitations, and many features are not yet supported.

[According to the manual as of 2.78# series SSS is not supported in AMD cards as stated in the Render Features page.

That may change in future, Mai Lavelle's work on Cycles Split Kernal may make it to 2.79, and may bring new features with it including SSS for OpenCL