ID 376773 - Group Masks with alpha textures are not masking parts of a normal map correctly when it is below the Group Mask in the hierarchy

​Problem summary
Group Masks with alpha textures are not masking parts of a normal map correctly when the normal map is below the Group Mask in the hierarchy of the Shader Tree. 

Any Layers that are outside the material group can be seen through the affected parts of the normal map, when not using the "Project Through" setting in the Front Culling option in the Texture Locator Properties of the Group Mask. 

Customer reported version
Modo 12.1v2

Customer reported platform
Windows 10 

Steps to reproduce

1) Open Modo and create any round mesh. Assign a material to the mesh and change the colour to black. 

2) Move the default Scene Camera to face the mesh. 

3) Go the Shading tab and add a Constant in the new material and set its Layer effect to "Diffuse Color".   

4) Add an Image Map and load the attached alpha texture. Set its Layer Effect to "Group Mask". 

5) Add another Image Map and load the attached normal texture. Set its Layer Effect to "Normal"

6) In the Properties for the both of the Image Maps, change Projection Type to "Planar" and Projection Axis to "Z". 

7) In the same Properties, change the Front Culling option to "Cull Backfacing". 

8) Put all of the created shading items in a Group. The material hierarchy should now be organised like in the image below, making sure that the normal map is below the Group Mask. 

9) Start to render the scene by pressing "F9". 

10) In the rendered frame below, some parts of the normal map are not correctly masked. The colour of the material that is outside the material group can be seen through the affected areas.

​​Workaround
Put the normal map above the Group Mask in the hierarchy and the mask appears to be correctly put on the normal map. 

Reproduced by support

This bug has been reproduced in:

Modo 12.2v1 - Windows 10 - MacOSX 11.13 - CentOS 7 
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 - MacOSX 11.13 - CentOS 7

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

Expected behaviour
Group Masks should mask all parts of a normal map correctly when any "Front Culling" setting is set, regardless of the position in the hierarchy. 

Actual behaviour
The Group Mask is not masking some parts of a normal map correctly and any layers outside the material group can be seen through those affected areas.