flush_rules(); only works when there is an echo in function

hey guys,

I got a very strange problem. I want to add some custom rewrite-rules to my theme in order to get custom pretty permalinks. I must pass variables in the URL so I can adjust the content according to what the user selects in a submenu. In order to do this I use pretty much the standard procedure as described in the Codex.

It actually works, BUT ONLY if I add a php echo to the function my_flush_rules where I call $wp_rewrite->flush_rules().
If I leave out the echo or just echo an empty string it stops working. In this case no more variables are passed on and the urls aren’t rewritten anymore, so I suppose the new URL-rewrite rules simply aren’t applied.

As you may have guessed I do not want to echo some strange text just so url-rewriting works properly. What did I do wrong?

I’m totally stuck here, can anyone help?

Here’s my code from the functions.php:

add_filter('rewrite_rules_array', 'my_rewrite_rules');
add_filter('query_vars','my_rewrite_query_vars');
add_filter('init','my_flush_rules');

function my_flush_rules(){
	echo "whatever";
	global $wp_rewrite;
   	$wp_rewrite->flush_rules();
}

function my_rewrite_rules( $rewrite_rules ) {

    $new_rules = array(
		'(test)/([a-z]+)$' => 'index.php?pagename=$matches[1]&mycategoryvar=$matches[2]',
		'(test)/([0-9]+)$' => 'index.php?pagename=$matches[1]&mypagevar=$matches[2]',
		'(test)/([a-z]+)/([0-9]+)$' => 'index.php?pagename=$matches[1]&mycategoryvar=$matches[2]&mypagevar=$matches[3]'
	);
    $rewrite_rules = $new_rules + $rewrite_rules;
    return $rewrite_rules;

}

function my_rewrite_query_vars($qvars)
{
    array_push($qvars, 'mypagevar', 'mycategoryvar');
    return $qvars;
}

And here’s my code from the .htaccess (I currently develop the page on my local XAMPP installation – hence the url):

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /wordpress/
RewriteCond %{REQUEST_URI} !\..+$
RewriteCond %{REQUEST_URI} !/$
RewriteRule (.*) https://localhost/wordpress/$1/ [R=301,L]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /wordpress/index.php [L]
</IfModule>