This is intentional - the idea of Filtered Item List is that it shows a list/grid of links to pages below the Parent Item(s) that match the criteria.

So for example, you might create a "Blog" page on your site, on which you add a Filtered Item List to show links to all pages that you add below that page in the site map.

Here are a few examples of it in use.

Demo Site Homepage - the "Features" list in the right column is a Filtered Item List showing all pages in the Features section of the site. It is configured as a List Group showing Short Title of each page.

Demo Site Features Page - the grid on this page is a Filtered Item List configured as a 3 Wide Grid, showing Title and Subtitle, with Related Image, using Medium size image and 3x1 aspect ratio for the images.

The 'Showcase' page on the main Voice site also uses a Filtered Item List to show links to sites.

In all cases, the things in the list/grid are content pages on the site, and the Filtered Item List is showing links to them. The pages themselves are not added to the Filtered Item List configuration, just the Parent folder that contains the pages.

Hope this helps!

Thanks

Joe

PS. If you do want to control exactly what goes into the list/grid then you can use the Item List includelet and explicitly choose which pages you want to include.