Hook parent_file

[drashka]

Hello,
I have a problem with one of the hooks on the admin side menu and I think it's a bug.
I'm trying to add a link to add a custom post type under an ACF option page. I've managed to set it up, but the menu doesn't display level 1 in current correctly. So I used this hook available in /wp-admin/menu-header.php line 38: {{{#!php
<?php
$parent_file = apply_filters( 'parent_file', $parent_file );
}}}

This filter does modify the parent_file, but on line 50, the call to the get_admin_page_parent function overloads the data I've hooked into it. Is this intended? If I pull up the function call, the problem is solved.
Thanks in advance!
Mathieu