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
example file: baked_result_too_bright.blend
open the file, DON'T change selection, hit bake.
for illustration attaching screenshots from this file