Project tangent to surface does not result in correct surface boundary in Rhino 6

In Rhino 5, when a line is projected on a vertical surface in top view, the resulted projection corresponds to the surface boundary.
In Rhino 6, the top and bottom edge are off by more than 100mm, well outside the set tollerance.
See image and (rhino 5) example file with one line and one surface.

project_curve_on_surface_edge(in top view).3dm (57.8 KB)

We see this problem for a lot of surfaces every time we project a grid of lines onto objects in Rhino 6, while I have never seen this happen in rhino 5.
On the surfaces that are not vertical, the project lines function works without problem.

I searched the forum and looked through many project issues but could not find anything similar to our problem.
We use this function very regularly to project many named curves onto hundereds of surfaces and then export sections by curve name, so using duplicate border for some of the surfaces is not very practical.

Both “section” and “contour” work correctly, but we really want the curve name to end up in the section. (I already reported and have a workaround script for Rhino 6 to make project to surface preserve the curve name, as in does in Rhino 5.)

Is there a way to impove the project tollerance for this situation?

Hello - I see this - I don’t think I’ve ever projected a curve this way… I can see how it could happen easily enough other than how you’ve set it up here though. I’ll add it to the pile - thanks.
Section works on the single surface edge-on case so I suspect this is an easy fix.
I see that is does work as expected when the line is part of a rectangle that corresponds to the face of a solid -



yes, I just updated my post before reading yous. countour works too.
If I rebuild the line to 3 points the result is a little better, but still well outside the tollerance.

RH-46171 is fixed in the latest Service Release Candidate

…and RH-46171 is fixed in the latest Service Release.