ID 360733 - Minor GL artefacts when enabling Merge Vertices for the Mirror mesh operation.

Problem summary
The Merge Vertices setting for the Mirror mesh operation can cause artefacts to appear when viewing the Base Mesh layer. These artefacts are the ghosted faces of the Mirror mesh overlapping the Base Mesh badly:

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Customer reported version
modo.n/a

Customer reported platform
windows7

Steps to reproduce
1) Open the attached scene file. It contains a rounded Cube mesh with a procedural stack of the Mirror mesh operation. 

2) The Base Material assigned to the mesh is a bright green. This material affects the Base Mesh. 

3) Go to System > Preferences > Defaults > Procedural Modeling and change the Color of the Ghosted Mesh Drawing (the Mirror operation) to a bright red, and set it to 100% Opacity - this helps with visibility.

4) In the Mesh Ops tab of the Item list, select the Base Mesh layer. You will see the ghosted mesh from the Mirror operation intersecting the Base Mesh.

5) Select the Mirror operation and disable the setting "Merge Vertices". Switch back to the Base Mesh and you will no longer see the intersection - the ghosted mesh is now displaying as desired. 

Reproduced by support
This bug has been reproduced in:

Windows 10
12.1v2 
12.0v1
11.2v3
11.1v1
11.0v3
11.0v1

macOS
12.1v2
11.0v1

Earliest version tested
11.0v1 - This feature did not exist before this version

Expected behaviour
When viewing the Base Mesh with Merge Vertices enabled, the ghosted Mirror operation should not intersect through the Base Mesh - it should align itself with the Base Mesh, as is the case when the Merge Vertices setting is disabled.

Actual behaviour
When viewing the Base Mesh with Merge Vertices enabled, the ghosted Mirror operation can intersect through the Base Mesh causing artefacts.