if a clipping plane is copied than no second clipping plane popup at the asset editor. But at the object properties independent parameter can be set, for example one to “exclude” and the other to “include” mode. So, both clipping planes seems to be independent, but are using the same asset. Confusing - best each get an own asset.
Thank you for your feedback. This is an expected behavior.
What happens is that V-Ray properties are attached to Rhino objects. Following your example, when copy-pasting the widget in the viewport, two Rhino objects with the same V-Ray settings are present in the scene. In addition to this, Include/Exclude options are preserved for each object. If you want to have two different V-Ray Clipping Plane settings go to the Rhino Properties Panel > V-Ray tab and use the Make Unique option.
Regarding deleting a Clipping plane widget from the viewport - it is kept in the Asset Editor because it can be assigned to another Rhino object.