ID 378101 - "Assign Selection Set" Operator on a mesh corrupts UVs when its merged into another mesh.

Problem summary
"Assign Selection Set" Operator on a mesh corrupts UVs when its merged into another mesh. For Example:

​

​

Customer reported version
modo.12.2v1

Customer reported platform
windows10

Steps to reproduce
1) Open Modo.
2) Open the attached Scene via "File Open"
3) Select the "Left Viewport Toggle" option (In Modo 12.2 and above) or the UV layout.
4) In the UV viewport, select UV > Texture to show the texture map.
5) Select the "Source" mesh item. The UVs should appear as they do on the first image above.
6) Select the "Merged" mesh item. The UVs should appear as they do in the second image above.
7) Expand the "+" next to "Source" and disable "Assign Selection Set."
Result: The UVs are no longer corrupted on the Merged mesh item.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
12.2v1 - Windows 10, OSX 10.13.5

Unable to reproduce bug in:
12.1v2 - Windows 10, OSX 10.13.5

Earliest version tested
12.1v2 - Windows 10, OSX 10.13.5 - This issue no longer appears in this version and has regressed

Expected behaviour
Assign selection set operators should not affect the UV map on any merged meshes.

Actual behaviour
Assign selection set operators corrupt the UV map on merged meshes.