Material Network Shader Input and Custom Bind Export Conflict

[syntheticperson 1]

I want to be able to export custom attributes from inside my own copy of the classic shader.
I also want to be able to feed inputs into my custom shader, at the Material Network level.
However, there appears to be a conflict.
When there are no inputs at the Network level, then the custom attribute is visible in the extra image plane in my mantra node.
However, as soon as I connect anything to any input at the Material Network level, then the custom image plane becomes black/zero.
Any ideas?
I have documented the example hip file with post-it notes, from scene level all the way down to the shader level for navigation.
thanks

customShaderMaterialArbitraryExportBug.v01.hipnc