Intersect fancy behavior not documented

Rhino 4.0 SR 9.

I have a surface and a curve. When I ask for the intersection of the two, I get an intersection at a place where the curve and the surface visibly do not intersect. I strongly suspect that this is because Intersect has fancy behavior like Split, except that the fancy behavior of Split is documented, while the documentation of Intersect says nothing about this.

I spent an hour or two being confused about this, plus the time I am taking to tell you about it.

(1) Is there something I am missing, or is my suspicion correct??

(2) If my suspicion is correct, let me jump up and down and insist that this is a bug.

Definition of a bug: Incorrect behavior. What is “incorrect”? Answer: Different from the documentation.

(3) Here is the example: example3.3dm (3.5 MB)

(4) I would very much like a switch on Intersect (and Split too) that turns off the fancy behavior. In my case, I was using Intersect to check that the relation of the curve and the surface was what I wanted. The fancy behavior made this check impossible.

Hi David - thanks for the report & file - for now, ShinkTrimmedSrf on the surface before intersecting.