I can give you a work-around that may or may not be useful to you. Replace the line/spline/line by a Fit Spline. Then you will get just one face instead of three. This, unfortunately may cause you worse problems. You won't be able to put a sketch on the face, as neither end is now a planar surface, like they were in the original. You won't have edges where the lines met the spline. You may break other features downstream that were children of the original faces.
As far as your subsidiary question, I've been wondering why you are still driving yourself crazy with a program that you obviously loathe. You posted here some time ago under your name. (Philippe Carette?). When the posts stopped, I assumed that you had quit the job that required you to use SolidWorks or convinced your boss to switch to a different CAD program. But now you are back, so I was wrong. What is the real story?
a composite curve works, but this intersection, where parameters are lost on the way, is really awful.
Perhaps the reason why the intersection isn't updated, if the surfaces are modified.
It's a big problem, imo, and it's strange that a product like SW is staying with such bug.
I hope that SW team is totally rewriting the program, because the list of misbehaviours I listed since 2 weeks is really impressive !!!
About my story, I lost my previous usr:pw, so I re-registered with those ones..
I only use SW, as dilettante, for personal projects, since I do other else than CAD in another life
I saw that there was a more complete edition with this summer E (with simulation features) , so I am trying to improve my mechanical simul with this version.
Well, as it turns out, they are completely rewriting the program, and have been for several years now. This fills some of us with trepidation, as we are not as unhappy as you with the existing program and wonder how much we will like the new program.
Wow, you do this for amusement. I'm amazed! I don't think I would have the patience to put up with a program that caused me as much pain as SolidWorks seems to cause you. I don't think I could do it for work, let alone for pleasure. But I'm glad that you keep trying. It is good for the people at SolidWorks to hear about the inconsistencies and problems.