This is relevant to the OctaneRender for Rhino plugin.
If I assign a Custom material to a box, as follows (with the Octane Material assigned to the Sphere):
then I select the box and ctrl-C then ctl-V, I end up with:
Note that an extra Octane Material has been created. I can see this happening in the RenderContent_ContentAdded event.
Why does this happen please, and how can I fix it?