Multiple intersections instead of one

Why are these surfaces getting multiple intersection curve results instead of just one curve each?
Try intersecting the black surface with the red (Rhino gave me 5 intersections) and the black with the blue (another 5 one time, 6 intersections another time). And the intersections do not even make a continuous line.
Is there a glitch or error with the surfaces?
WhyNIntersections.3dm (187.7 KB)

Seems like a bug.

Hi Matt - my guess of the moment is that it’s because the intersection falls right on an isocurve, well knot in this case, of one of the inputs - it looks like the surface may have been extended with Type=Line at some point, is that correct? There is a fully multiple knot (= kink if you move a control point there) as a consequence. If I split that surface back at the knot and extendSrf > Type=Smooth out again as you have it, the intersection is as expected.

WhyNIntersections_PG.3dm (158.6 KB)


I agree. It’s a bug. RH-65953 Missed segments in SSX result

Thanks all, for confirming that it’s a bug.
Pascal - yes, I used ExtendSrf and must have not have changed “Type=Line” to “Type=Smooth”. That forgetfulness would also explain minor geometric issues I had elsewhere when I was extending other surfs.