ID 381312 - Duplicating a source item causes the duplicated item to be added as a source to a merge mesh operation.

Problem summary
Duplicating a source item causes the duplicated item to be added as a source to a merge mesh operation.

Customer reported version
modo.12.2v1

Customer reported platform
windows10

Steps to reproduce
1) Open Modo.
2) Hold "Ctrl" and click the cube tool to create a cube primitive.
3) Press "n" to create a new mesh layer.
4) Select the "Mesh operations" tab in the item bin of the Model Layout.
5) Select Add Operator > Merge Meshes.
6) Expand the list of source items and add the mesh layer containing the cube as a source.
7) Select the cube and press "CTRL + D" to duplicate it.
Result: The duplicated cube will be added to the Sources list for the merge mesh item.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
12.2v1 - Windows 10, OSX 10.13.5
12.1v2 - Windows 10
12.0v1 - Windows 10
11.2v3 - Windows 10
11.2v1 - Windows 10
11.1v1 - Windows 10
11.0v3 - Windows 10
10.2v4 - Windows 10, OSX 10.13.5

Earliest version tested
10.2v4 - Windows 10, OSX 10.13.5 - This issue appears to be in all versions of the product

Expected behaviour
Modo should not automatically add duplicated meshes into a merged mesh.

Actual behaviour
Modo automatically adds duplicated meshes into a merge mesh operation if the source is already listed.