Problem with WP Rewrite

I need to rewrite an address like this:

http://example.com/galleria/artist-name

so that it goes to the gallery.php page with a variable containing ‘artist-name’. I used the same syntax as in the wp rewrite documentation and while it works fine on my local wordpress install, on the real server it has a strange behavior: the original URL is accepted (i.e. it doesn’t end in a 404) but it gets rewritten to

http://example.com/gallery

(I mean actually rewritten in the browser’s address bar) and the variable is not set.

Rules used:

// REWRITE RULES (per gallery) {{{
add_filter('rewrite_rules_array','wp_insertMyRewriteRules');
add_filter('query_vars','wp_insertMyRewriteQueryVars');
add_filter('init','flushRules');

// Remember to flush_rules() when adding rules
function flushRules(){
    global $wp_rewrite;
    $wp_rewrite->flush_rules();
}

// Adding a new rule
function wp_insertMyRewriteRules($rules)
{
    $newrules = array();
    $newrules['(galleria)/(.*)$'] = 'index.php?pagename=gallery&galleryname=$matches[2]';
    return $newrules + $rules;
}

// Adding the id var so that WP recognizes it
function wp_insertMyRewriteQueryVars($vars)
{
    array_push($vars, 'galleryname');
    return $vars;
}

WordPress 2.9.2 both in my local test environment, and on the running online server. What can cause this behavior?

Thanks