Currently post types and taxonomies that are registered to support a specific subset of taxonomies are not being fully respected by the plugin. So when a post type like pages which doesn't support categories or tags is queried against the collection, only empty edges will be found even if pages have been assigned a category via wp_set_object_terms(). We should change $allowed_post_types and $allowed_taxonomies to be a filterable value and more specific to each taxonomy or post type. We can have all of the values stay the way they are right now, but we can add filters that will take a subset of those allowed types and which will remove and fields on the taxonomy/post type that will go no where.