Here's a simple fully-defined sketch of a hexagon that I want to extrude into the hex head of a stud.  The original vertical line on the left side has been replicated using Circular Sketch Pattern to complete the hexagon:

Here's what happens when I try the Extruded Boss/Base feature on the sketch:

Apparently SW interprets the sketch as open -- the original vertical line appears unconnected to its circular-patterned neighbors -- and forces a thin-feature extrusion, which of course I don't want.  Yet the Measure tool tells me that each of the six full lines intersects its neighbors, and I can't see any extraneous lines that are not "for construction."  Is there something wrong with using Circular Sketch Pattern in this context?

I'm running SW Premium 2016 SP5.0 under Windows 7 SP1.  Part file provided on request.  Can anybody point out my mistake? -- John Willett