ID 364152 - The Group Mask layer effect does not mask the dissolve layer effect correctly

Problem summary
The Group Mask layer effect does not mask the dissolve layer effect correctly. The Group Mask layer effect works with other layer effects.

Customer reported version
Modo 12.1v2

Customer reported platform
Windows 10 

Steps to reproduce
1) Create a primitive and assign a material to it. 

2) Create a Group Mask.

3) Assign a alpha image to a layer, change effect to Dissolve.

4) Rearrange so that the Dissolve layer is underneath the Group Mask in the Shader Tree.

5) Render the primitive to see that the Dissolve layer is not being masked by the Group Mask. 

Workaround
To mask the Dissolve layer, you can use a Layer Mask instead: 

1) Duplicate the Mask Group and change the effect to "Layer Mask".

2) Place the Layer Mask under Dissolve layer.

3) Render the primitive to see the Dissolve layer being masked by the Layer Mask. 

Reproduced by support
This bug has been reproduced in:
Modo 12.1v2 - Windows 10 - CentOS 7 - MacOSX 10.13
Modo 12.1v1 - Windows 10
Modo 12.0v1 - Windows 10
Modo 11.2v3 - Windows 10
Modo 11.1v1 - Windows 10
Modo 11.0v3 - Windows 10
Modo 10.2v4 - Windows 10 - CentOS 7 - MacOSX 10.13

Earliest version tested
Modo 10.2v4 

Expected behaviour
Group Mask correctly masks the Dissolve layer. 

Actual behaviour
Group Mask does not mask the Dissolve layer.