Hello Bill,
It looks like it is applied – the link says “taxonomy=category&post_type=article.” I think I just misunderstood what the [display-posts] shortcode with custom post type is supposed to do. When used it does display only posts from the custom post type, with the correct categories appended. I think it is working at intended, I simply was expecting something else.
Sorry, I am a bit of a newbie with wordpress, still learning and working my way around day by day. Thanks again for your reply!
TL