Hi Steve, do you mean in particular on mitered corners for 3d swoopy path curves?

It is pretty difficult for the miter intersection to work in those cases, and yes it is possible for things that are sensitive to have different results at different scales when refinement tolerances are involved.

Also with 3D swoopy curves, there is are some fundamental geometric problems with trying to make an extension + intersection type mitering mechanism to actually work at all, particularly when the profile curve is not a circle due to the twisting action as the profile travels along the rail. See here for some previous discussion on that:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3575.4

In the future I think that I'm going to switch to a different technique when you try to sweep along a path that is made up of curvy 3D paths, where it will automatically place some scaled and angled profiles for you at the corner point rather than trying to do an actual extension and miter cut.

- Michael