pjm, a conclusive test would be to reset your polar chart, and clear the data in sbsplotter, then run both for a day.
You can then save an OUT file from sbsplotter, put that into your outlines folder, and then display the outline of the "true" polar chart from sbsplotter in ANRB.
This will also be a useful technique to test the fix when Airnav finally fix this bug.