Operating system and graphics card
Windows7, Nvidia GTX 1060
Broken: 2.78a e8299c8
Short description of error
trying to bake mixed shader with transparency with no color option generates too bright area.
non-100% transparency mixing or not transparent materials never generate these issues.
I use these techique for texturing, as seen in the file.
Exact steps for others to reproduce the error
open the file, DON'T change selection, hit bake.
for illustration attaching screenshots from this file