Problems with Sweep 1 Rail. Bug?

I’m getting a result with Sweep Rail that I didn’t expect. Is there a solution please?

Here is my rail which is made up of a single polyline. At each end is a circle. One end’s circle is larger than the other.

What I want is a single cone that snakes its way from one end of the rail to the other, but what I get are three cones. That doesn’t happen if the polyline are curvy instead of angled.

BTW, I should add that I can’t even trim the objects to get the desired shape.

Apologies. Answer was to choose ‘untrimmed mitres’.

Yeah, trimmed miters on tapered and especially non-planar paths is rarely going to work.

-P