I find that once I have created a custom Cplane in the Perspective view I can no longer revert back to it.
This is in spite of the tooltip displayed in the dropdown menu (View< Set View < Perspective) that states “Set the active view to the default perspective view”.
That’s why I didn’t understand your question, you were referring to the Construction Plane, not the view (but Zsimon did get it! ) . There is a very relevant difference between the two, and I would advise to get familiar with that difference because in my opinion that is one of the basics in designing with Rhino.