Windows and Debian Linux
The rendered image is significantly different on different platforms.
However, it seems that the output of Version 2.74 on Debian Linux is quite similar to the Windows 2.78 output, so this might be a regression.
The transparent material uses Glass (GGX), Transparent and Translucent shaders. The surrounding copper object uses Fresnel and Glossy (GGX).
I may be able to strip this down to a simpler scene this evening.