I think what you're telling me is that if I have sharpening specified in the Edit/Preferences/Printing Options dialog, and also have sharpening specified in the Print Filter, that both those sharpening steps will be applied upon printing the image. Is that correct?
Yes. So what you should do is set the print sharpening by just changing the "Sharpen" value under Printers and Settings on the main window. Leave sharpening out of your print filter(s) because it's best to do that in the "Sharpen" feature.
Adding sharpening in a print filter will not work as well because that will sharpen every image the same amount regardless of how big you intend to print it, what it's resolution is, etc. If you use the "Sharpen" dropdown on the main window, that knows how to keep consistent sharpening across any print size/resolution.
Mike