0
Not a bug
Alpha Channels Breaks Shader
Every time I try to use an Alpha Channel from a Diffuse or Normal map, the output turns pink and I get a console full of errors.
Customer support service by UserEcho
R -> G
G -> A
B -> -
A -> -
It puts the red channel in the green channel of the new texture.
It puts the green channel in the alpha channel of the new texture.
It dumps the data in B and A.
When it's in the shader, the normal is unpacked using G and A, and then it reconstructs the Z (B) channel of the normal map. Unity does this to increase the precision and quality of the normal maps, but the data in the alpha channel is lost in the process.
You can do your own normal map unpacking. If you add a Texture 2D node, and use a texture that isn't marked as a normal map in the texture import setting, and don't mark it as a normal map in the Texture 2D node either, you can unpack RGB using the Remap node (R + LMB), set it to [ 0 to 1 ] -> [ -1 to 1 ], and then plug it into the normal input. With this approach, you're saving the alpha channel as well :)
Hope that answered your question!