ID 557046 - Item Shaders attached to items do not work correctly and can become unstable.

Problem summary
Item Shaders attached to items do not work correctly and can become unstable.
 
Customer reported version
modo.16.1v8
 
Customer reported platform
windows10
 
Steps to reproduce
 
1) Open Modo and create a Simple Plane and a Simple cube.

2) Right-click the Cube and select Shader > Create Item Shader.

3) Select Render > Preview and disable Cast Shadows notice that the Cube is still casting a shadow on the plane.

4) Go to the Shader Tree and move the Base Shader item below and then back above the Base Material item. Notice that disabling and enabling Cast Shadows on the Item Shader attached to the Cube now works as expected.
 
5) Delete the Shader Item attached to the cube and Modo crashes.
 
Expected behaviour
The Item Shader should work by default and shouldn't crash when deleted.
 
Actual behaviour
The Item Shader doesn't work by default and once this is correct results in a crash if it's deleted.
 
Workaround
The Item Shader can be made to work by moving the Base Shader item below and then back above the Base Material item. 
 
Note that this does result in a crash if this Item Shader is deleted.
 
Reproduced by support
 
This bug has been reproduced in:
16.1v8 - Windows 10, macOS 13 -regression
 
Unable to reproduce bug in:
16.1v7 - Windows 10, macOS 13
 
Earliest version tested
16.1v7 - This issue doesn't appear in this version and has regressed.