ID 358316 - "Crease by Smoothing Angle" option is overwritten by materials higher in the layer stack

Problem summary
The "Crease by Smoothing Angle" option can overwrite materials lower in the layer stack, even when the material is not assigned to the same mesh items. 

Customer reported version
modo.12.1v1

Customer reported platform
10.13

Steps to reproduce
1) Open Modo.
2) Select file>import and import the attached files.
3) Select Vertex Map>Vertex Normal Tools to open the Vertex Normal Tools window.
4) Select the Mesh Item, then select "Convert to Hard Edges." Enable all options.
5) Switch the viewport to "Reflection" to see the issue more clearly.
6) Switch to polygon selection mode by pressing "3"
7) Select the two polygons composing the rounded edge and click "harden" in the Vertex Normal Tools window.
8) In the item bin, select the shading tab.
9) Select the material item nested under "corner"
10) Uncheck "Crease by Smoothing angle."
Result: the entire mesh remains "hardened."
11) Select the eyeball to the left of "other_unrelated_materials" to hide the material.
Result: the two polygons selected in step 7 update, even though the "higher_material" is not assigned to them.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
12.1v1 - Windows 10, OSX 10.13.5

Earliest version tested
12.1v1 - Windows 10, OSX 10.13.5 - This feature did not exist before this version
Expected behaviour
Unrelated materials should not propagate settings to other materials.

Actual behaviour
The "Crease by Smoothing Angle" option can propagate to materials lower in the material stack, even if they are not assigned to the same items.