Hierarchical custom post type - can't specify parent

<?php
/* Register Custom Post Type for CD */
add_action('init', 'cd_post_type_init');
function cd_post_type_init() {
  $labels = array(
    'name' => _x('CD', 'post type general name'),
    'singular_name' => _x('cd', 'post type singular name'),
    'add_new' => _x('Add New', 'CD'),
    'add_new_item' => __('Add New CD'),
    'edit_item' => __('Edit CD'),
    'new_item' => __('New CD'),
    'view_item' => __('View CD'),
    'search_items' => __('Search CDs'),
    'not_found' =>  __('No CDs found'),
    'not_found_in_trash' => __('No CDs found in Trash'),
    'parent_item_colon' => ''
  );
  $args = array(
    'labels' => $labels,
    'public' => true,
    'publicly_queryable' => true,
    'show_ui' => true,
    'rewrite' => true,
    'query_var' => true,
    'capability_type' => 'post',
    'hierarchical' => false,
    'show_in_nav_menus' => false,
    'menu_position' => 1000,
    'supports' => array(
      'title',
    )
  );
  register_post_type('cd',$args);
}

/* Register Custom Post Type for Track */
add_action('init', 'track_post_type_init');
function track_post_type_init() {
  $labels = array(
    'name' => _x('Track', 'post type general name'),
    'singular_name' => _x('Track', 'post type singular name'),
    'add_new' => _x('Add New', 'Track'),
    'add_new_item' => __('Add New Track'),
    'edit_item' => __('Edit Track'),
    'new_item' => __('New Track'),
    'view_item' => __('View Track'),
    'search_items' => __('Search Tracks'),
    'not_found' =>  __('No Tracks found'),
    'not_found_in_trash' => __('No Tracks found in Trash'),
    'parent_item_colon' => __('CD'),
    'parent' => __('CD'),
  );
  $args = array(
    'labels' => $labels,
    'public' => true,
    'publicly_queryable' => true,
    'show_ui' => true, //false - to hide from the admin area menu
    'rewrite' => true,
    'query_var' => true,
    'capability_type' => 'post',
    'hierarchical' => true, //allow parent pages
    'show_in_nav_menus' => false,
    'menu_position' => 1000,
    'supports' => array(
      'title',
      'page-attributes'
    )
  );
  register_post_type('track',$args);
}
?>