Does Not Work

Have you added the 'submenu' => 'Something' parameter to your call to wp_nav_menus?

Your plugin works great for Posts or Custom links added to a WP menu, but does not work for Pages added to menus.

To fix…

Line 42 in submenu-filter.php is originally:

$item->slug = sanitize_title_with_dashes($item->post_title);

When you add pages to a WP menu, they don’t have a post_title property.

Simply change to use the ‘title’ property since all object types added to a WP menu have this property.

New Line 42:

$item->slug = sanitize_title_with_dashes($item->title);

I actually found and fixed the same problem only a few days ago, and have yet to publish a new version.

I’ve published version 1.2 which should fix this.