Permalink leads to wrong attachment

Am I correct in my assumption, that the attachment slugs should be unique in WordPress? If it is true, I can see an obvious flaw in wp_insert_attachment() function in /wp-includes/post.php:

Currently the unique name check looks like this:

$post_name_check =
	$wpdb->get_var("SELECT post_name FROM $wpdb->posts WHERE post_name = '$post_name' AND post_status = 'inherit' AND ID != '$post_ID' LIMIT 1");

if ($post_name_check) {
	$suffix = 2;
	while ($post_name_check) {
		$alt_post_name = $post_name . "-$suffix";
		$post_name_check = $wpdb->get_var("SELECT post_name FROM $wpdb->posts WHERE post_name = '$alt_post_name' AND post_status = 'inherit' AND ID != '$post_ID' AND post_parent = '$post_parent' LIMIT 1");
		$suffix++;
	}
	$post_name = $alt_post_name;
}

So the name check uses different SQL queries for the first check and for all subsequent ones. If indeed the attachment slugs should be globally unique, then the second query shouldn't have the post_parent check.

Like this:

$post_name_check =
	$wpdb->get_var("SELECT post_name FROM $wpdb->posts WHERE post_name = '$post_name' AND post_status = 'inherit' AND ID != '$post_ID' LIMIT 1");

if ($post_name_check) {
	$suffix = 2;
	while ($post_name_check) {
		$alt_post_name = $post_name . "-$suffix";
		$post_name_check = $wpdb->get_var("SELECT post_name FROM $wpdb->posts WHERE post_name = '$alt_post_name' AND post_status = 'inherit' AND ID != '$post_ID' LIMIT 1");
		$suffix++;
	}
	$post_name = $alt_post_name;
}

I tried the modification above, and the attachment slugs are unique now.

Patch based on futurix's comment added.