Post_per_page -1 returns only half the results

As hinted by the comments I replaced the query_posts by a WP_Query query.

$args=array(
    'post_type' => 'restaurante',
    'posts_per_page' => -1,
    'meta_key' => 'restaurante_municipio',
    'orderby' => 'meta_value',
    'order' => 'ASC');
$the_query = null;
$the_query = new WP_Query($args);
if ( $the_query->have_posts() ) {

    $total_results = $the_query->found_posts; 
    echo '<p><b>Restaurantes: '.$total_results.'</b>';
    while ( $the_query->have_posts() ) {
        $the_query->the_post();
        ...
        ..
        .
    }
}
wp_reset_postdata();

Now it is working