SoftEditCurve method doesn't behave as described in API

using the Curve.SoftEditCurve methode in one oy my projects I am surprised to see it does not deliver the result I was expecting looking at the Rhino 6 Documentation ( or the methode description in the API docu.

Attached a model showing the methode behavior. It looks there is a complete different algorithm working in the background as in the online documentation/examples.

What is wrong here? Am I mistaking something? (14.7 KB)