Issuu: If article is Featured Aticle or not and not selected in any menu items, it will show on the Home page. And the Home page is using the default template. Beside that, the slideshow is assigned to Home page. Because of that, this article will show with layout "default" and under slideshow.
My suggestion here is that you can create a new menu called 'hidden menu' (if you don't want to show in frontend of your site) and create its menu item. Then you assign above THE category or one of these articles to this new menu item. Also make sure that you don't assign any module to this new menu item. After that, you go to frontend > refresh your page > click to open article you assigned, it would redirect to details article page.
