Brep CreateFromSweep Fails for shallow Triangles

Good Morning All,

Using Brep.CreateFromSweep (in C#) I try to sweep the little blue line around the inside of the triangle I get a rather strange result - anyone know how to avoid this? I was expecting the sweep to stay inside the triangle.
Brep.CreateFromSweep(curve, line, true, 0.0001)

I have explored the SweepOneRail but had other problems with that and “Note, this class has been superseded by the Rhino.Geometry.Brep.CreateFromSweep static functions.”

BrepSweepFail.3dm (46.7 KB)