I can't reproduce this if I set storages as described in the tutorial.
Which is not the same as your setup - article related storage should NOT be empty or default, it should be custom-article-fieldxname[article_related_name] (with fieldX storage set to custom-article-fieldxname )
Please note that you need to create new field to have storage successfully set, if you change it e.g. from None to something else it won't work correctly. Also take care that you don't include aritcle related field anywhere in the form&content type, you should only use fieldX (with reverse being true on searches)