Redirect page renamed by plugin

Hi,

I created a php page in my root directory to be used instead of the suggested 404. However, when I save the setting with my new /example-page.php it is saved in the settings as example-page-php, converting the dot to a dash, making the suffix part of the main file name.

The result is a page not found 404 error. Is this the normal behaviour of the plugin? I tried saving example-page sans suffix as the name but the result was the same: 404 page not found…