category list orderby date problem

thanks to MichaelH now my website show most recent category list in sidebar but now the problem is when i create new category and add post up to 25 or 30, then all other category are disappear on my sidebar page only the one or two is appear

here is MichaelH code

<?php
// get 20 latest posts, display the categories used on those posts
$cat_array = array();
$args=array(
  'post_type' => 'post',
  'post_status' => 'publish',
  'posts_per_page' => 20,
  'caller_get_posts'=> 1
  );
$my_query = null;
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
  while ($my_query->have_posts()) : $my_query->the_post();
    $cat_args=array('orderby' => 'none');
    $cats = wp_get_post_terms( $post->ID , 'category', $cat_args);
    foreach($cats as $cat) {
      $cat_array[$cat->term_id] = $cat->term_id;
    }
  endwhile;
}
if ($cat_array) {
  echo '<p>List of categories used on 20 latest posts</p>';
  foreach($cat_array as $cat) {
    $category = get_term_by('ID',$cat, 'category');
    echo '<p><a href="' . esc_attr(get_term_link($category, 'category')) . '" title="' . sprintf( __( "View all posts in %s" ), $category->name ) . '" ' . '>' . $category->name.'</a><p> ';
  }
}
wp_reset_query();  // Restore global post data stomped by the_post().
?>

here is link http://wordpress.org/support/topic/399631