I have noticed that all of my concrete5 websites are displaying HTTP/1.1 301 Moved Permanently for page not found instead of 404.

Tested through:
http://404checker.com/404-checker...

I have followed all instructions including copying page_not_found.php to /single_pages.

This occurs on websites where I have modified config/site_theme_paths.php to allow for the site template to be used and other sites that do not.

All sites are running 5.6.3.2

I have tested it on different servers and all websites exhibit the same problem.

Does anyone else have the same problem.

Thanks