I am encountering an issue involving Revolve.

I can revolve the PART A contour shown below, and I can Revolve Part A + Part B in the same Revolve Feature.

But, it refuses to Revolve ONLY Part B.

This seems like a bug, because the excuse Solidworks is giving is that the Sketch is either "Open" or "Self-Intersecting" or "Intersects the Centerline".

So my confusion is, how can Contour A + Contour B build OK, But, contour B alone does not?

Is there a way to build B alone?

Thanks.