Re conflict with Kathy Darling’s Nav Menu Roles plugin, she writes:
Shazdeh, the author of Menu Item Visibility Control plugin had the [genius idea](http://shazdeh.me/2014/06/25/custom-fields-nav-menu-items/) to not wait for a core hook and simply add the hook ourselves. If all plugin and theme authors use the same hook, we can make our plugins play together.
Therefore, as of version 1.6 I am modifying my admin walker to *only* adding the following line (right after the description input):
<?php
// This is the added section
do_action( 'wp_nav_menu_item_custom_fields', $item_id, $item, $depth, $args );
// end added section
?>
I am then adding my fields to this hook. Ask your conflicting plugin/theme’s author to do the same and our plugins should become compatible.