First, i change the value of the parameter g_manage_user_threshold in my config_inc file but my manager have no access to the user administration.
I check in the permissions report: the manager have the right to manage users.

When i use url direct access with the page manage_user_page.php, it works. My manager can manage the users.
But the top menu link is not manage_user_page.php but manage_proj_page.php. And in the administration submenu, there is no link to manage_user_page.php.

So i verify in the php file and I found something :
Mantis v1.0.5.

In the html_api.php file, in the function print_manage_menu, i have this: line 639

PRINT '
<div align="center">';
if ( access_has_global_level( ADMINISTRATOR ) ) {
print_bracket_link( $t_manage_user_page, lang_get( 'manage_users_link' ) );
}

As you can see, the access check doesn't use the parameters like that:

if ( access_has_global_level( config_get( 'manage_user_threshold' )) ) {
print_bracket_link( $t_manage_user_page, lang_get( 'manage_users_link' ) );
}

So i have never have the sub menu with the user manage link if i am not a admin even if i update the parameters manage_user_threshold.

I think it's a bug no?