Arch Linux with AMD R9 285
Broken: 2.78 fb82948043
Short description of error
While rendering with a material using a NodeCustomGroup defined in an addon, unregistering the addon causes a crash.
Note that the attached "simplified" example (shader_test.py) works correctly! There's something going on with this complex shader that's causing a crash, and I unfortunately haven't been able to reduce it... Hopefully someone can do something with the crashlog.
Exact steps for others to reproduce the error
Load the attached ShaderNodeBsdfMetal.py, activate the "Conductive Fresnel Node" addon it defines, open the attached blend. Add a "Metal BSDF" node to the cube material, attach it to the output, then either hit F12 or shift-Z in the viewport. Deactivate "Conductive Fresnel Node" and witness the crash.
For the non-crash example, load the attached shader_test.py, activate the "Bug reproduction" addon it defines, replace the "Metal BSDF" node with a "Sample BSDF" (at the bottom of the list), attach it to the output, then hit F12 or shift-Z. Deactivate "Bug Reproduction" and witness the non-crash.