ID 379303 - The diffuse coefficient on full metallic materials does not render as black, if the diffuse colour of the principled shader is less than 1 in all RGB channels

​Problem summary
The diffuse coefficient on full metallic materials does not render as black, if the diffuse colour of the principled shader is less than 1 in all RGB channels. Should only one of the RGB channels be lower than 1, then the metallic material is rendered correctly as black. 

Customer reported version
Modo 12.2v1 

Customer reported platform
Windows 10 

Steps to reproduce

1) Open Modo. Create a plane and assign a material to it with a white diffuse colour.

2) Create a sphere and assign a material. Go to the Shading tab and change the new material's Shading Model to "Principled" in the Material Properties.  

3) In the same Material Properties, change the "Diffuse Color" to white by setting all RGB channels to 1. 

4) Increase the "Metallic" value to 100 % to blend the sphere's diffuse colour to black. 

5) In the Shading tab, select "Add Layer" and then add a "Diffuse Coefficient Output".

6) Press "F8" to open the Preview Render window. In the Preview Render, expand the "Effect" list and select the "Diffuse Coefficient Output". 

7) Start to render the selected "Diffuse Coefficient Output" and decrease one of the diffuse colour channels for the sphere's material. Notice that the diffuse coefficient on the sphere is black, which is correct when the "Metallic" value is at 100 %. 

8) Set the diffuse colours of the sphere's material so all of the channels are less than 1. The diffuse coefficient on the sphere is no longer rendered as black, which is incorrect when "Metallic" is set at 100 % and the diffuse colour channels of the principled shader are less than 1.

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Workaround
Unknown.

Reproduced by support

This bug has been reproduced in:
Modo 12.2v1 - Windows 10 
Modo 12.1v2 - Windows 10 
Modo 12.0v1 - Windows 10 
Modo 11.2v3 - Windows 10 
Modo 11.2v2 - Windows 10 
Modo 11.2v1 - Windows 10 

Earliest version tested
Modo 11.2v1 - This feature did not exist before this version.

Expected behaviour
The diffuse coefficient on metallic materials should always render as black if the "Metallic" value is set at 100 %. 

Actual behaviour
The diffuse coefficient on full metallic materials does not render as black, if the diffuse colour of the principled shader is less than 1 in all RGB channels.