Hi Rudy, I think it has something to do with your upper profile curve, it's slanted in relation to the curve's perpendicular and that means that things will try to transition to that type of slant as it moves from the lower profile which is oriented nicely perpendicular to the curve.

So the solution is to not use the upper profile at all, only select just the lower profile alone and do the sweep:





That will avoid having things morph to a slanted shape as they are traveling along the path, instead the shape will be a nice regular tube with a cross section perpendicular to the curve. Then the tip is automatically formed by corner mitering, that's where the one rail sweep automatically extends and intersects junctures at sharp corners. If you turn on the control points of this result you'll see the miter extensions:




Hope that helps!

- Michael