Just played with this a bit and think I have it working: https://github.com/tomusborne/WP-Show-Posts/commit/bb64b8886a7ae61181a0e5d550bd30f7831028c3
You can grab the entire function here and replace it with the one on your site: https://github.com/tomusborne/WP-Show-Posts/blob/master/inc/functions.php#L5-L31
Let me know 🙂