Thanks for your feedback!
The search results and display of them are NOT controlled by my plugin. My plugin "only" provides the widget with the search form and that searches within the post type. That is all you can do for search forms for custom post types.
I don't know your setup, which search.php or searchform.php your theme uses and how this works with custom post types. Also, there might be other plugins that maybe tweak anything to do with search...?
Are your download products that you want to search are all published? WordPress only searches within title and content (not in taxonomies or custom fields or whatever...).
You could test if your issue is still there when using other plugins that handle search control and display, like Relevanssi: http://wordpress.org/plugins/relevanssi/ --- let my search widget be active but install Relevanssi, configure it and see what happens.
Maybe that could help?
Thanks, Dave :)