Hi Timmy – The functionality that is setting your featured thumbnail is not setting the Featured Image. If you had a featured image, the standard WP function would display it. In other words, it does not have anything to do with our plugin – WP Recent Posts Pro – but rather that external featured image plugin being used.
Are you using the PREMIUM version of that plugin? As that is the only one that makes Flickr photos correctly set as Featured Thumbnails. It says so on the plugin’s page:
you can use external thumbnails from Flickr to make your site until 94% faster (premium feature);
If you are using the PREMIUM version, then please check your plugin’s configuration. As long as an image is correctly set as Featured, our plugin will 100% display it correctly.