How do you search for duplicate urls?
You can use the PHP function menu_get_item('path/in/question') to determine more about what module is responding to the url.

If the path is an alias, you may need to use drupal_get_normal_path($alias).

So if you use drush, you might run

drush ev "print_r(menu_get_item(drupal_get_normal_path('path/in/question'))"

That should return an array, which will likely have a 'page callback' element which will tell you the function (and hence, the module) that is handling that url.