Problems with custom taxonomy capabilities

Hi!

This is my first post to look for help. First of all, i have to apologyse about my english. And now, my hell call ??

I am registering a custom taxonomy into my functions.php, like this:

register_taxonomy('palabras-clave', 'sonidos', array(
		'capabilities' => array(
		'assign_terms' => 'edit_sonidos',
	        'edit_terms' => 'edit_sonidos',
		'manage_terms' => 'edit_sonidos',
		'delete_terms' => 'edit_sonidos',
		),
		'public' => true,
		'show_ui' => true,
         	'show_admin_column' => true,
		'show_in_nav_menus' => true,
		'show_tagcloud' => true,
		'hierarchical' => false,
		'label' => 'Palabras clave',
		'query_var' => true,
		'rewrite' => true,
		));

This taxonomy is linked with a custom post type and it is resgiter into functions.php too, like this:

add_action('init', 'sonidos_type_register');

		function sonidos_type_register() {

			$labels = array(
				'name' => __( 'Panel de sonidos' ),
				'singular_name' => __( 'Sonido' ),
				'add_new' => __( 'A?adir Nuevo' ),
				'add_new_item' => __( 'A?adir nuevo sonido' ),
				'edit_item' => __( 'Editar sonido' ),
				'new_item' => __( 'Nuevo sonido'),
				'view_item' => __( 'Ver sonido'),
				'search_items' => __( 'Buscar sonido'),
				'not_found' =>  __('No se encontró nada'),
				'not_found_in_trash' => __('No se encontró nada en la papelera'),
				'parent_item_colon' => ''
			);

			$args = array(
				'labels' => $labels,
				'public' => true,
				'rewrite' => true,
				'capability_type' => array('sonido', 'sonidos'),
				'capabilities' => array(
					'publish_posts' => 'publish_sonidos',
					'edit_posts' => 'edit_sonidos',
					'edit_published_posts' => 'edit_published_sonidos',
					'edit_others_posts' => 'edit_others_sonidos',
					'delete_posts' => 'delete_sonidos',
					'delete_others_posts' => 'delete_others_sonidos',
					'read_private_posts' => 'read_private_sonidos',
					'edit_post' => 'edit_sonido',
					'delete_post' => 'delete_sonido',
					'read_post' => 'read_sonido',
				),
				'map_meta_cap' => true,
				'hierarchical' => false,
				'menu_position' => null,
				'supports' => array('title'),
				'taxonomies' => array ('categorias-sonidos','sectores-industriales','periodos-industriales','palabras-clave'),
			  );

			register_post_type( 'sonidos' , $args );

Everything works fine, but the editor and contributor can not add ‘palabras-clave’, nor can see / select the existing ones.
I tried downgrading the level needed to manage terms in the custom taxonomy registered to ‘read’, but it still doesn’t work.

The capabilities modified are these:

// Capacidades del editor

	add_action( 'admin_init', 'modify_editor_capabilities' );

	function modify_editor_capabilities(){
	  global $wp_roles;
	  $wp_roles->add_cap('editor','read' );
	  $wp_roles->add_cap('editor','upload_files' );
	  $wp_roles->add_cap('editor','publish_sonidos' ) ;
	  $wp_roles->add_cap('editor','edit_sonidos' );
	  $wp_roles->add_cap('editor','edit_published_sonidos' ) ;
	  $wp_roles->add_cap('editor','edit_others_sonidos' ) ;
	  $wp_roles->add_cap('editor','delete_sonidos' );
	  $wp_roles->add_cap('editor','delete_others_sonidos' ) ;
	  $wp_roles->add_cap('editor','read_private_sonidos' ) ;
	  $wp_roles->add_cap('editor','publish_enlaces' ) ;
	  $wp_roles->add_cap('editor','edit_enlaces' );
	  $wp_roles->add_cap('editor','edit_published_enlaces' ) ;
	  $wp_roles->add_cap('editor','edit_others_enlaces' ) ;
	  $wp_roles->add_cap('editor','delete_enlaces' );
	  $wp_roles->add_cap('editor','delete_others_enlaces' ) ;
	  $wp_roles->add_cap('editor','read_private_enlaces' ) ;
	  $wp_roles->remove_cap('editor','list_users' );
	  $wp_roles->remove_cap('editor','create_users' );
	  $wp_roles->remove_cap('editor','edit_users' );
	  $wp_roles->remove_cap('editor','moderate_comments' );
	  $wp_roles->remove_cap('editor','manage_categories' );
	  $wp_roles->remove_cap('editor','edit_published_pages' );
	  $wp_roles->remove_cap('editor','edit_pages' );
	  $wp_roles->remove_cap('editor','publish_pages' );
	  $wp_roles->remove_cap('editor','delete_pages' );
	  $wp_roles->remove_cap('editor','manage_links' );
	  $wp_roles->remove_cap('editor','unfiltered_html' );
	  $wp_roles->remove_cap('editor','delete_posts' );
	  $wp_roles->remove_cap('editor','publish_posts' );
	  $wp_roles->remove_cap('editor','edit_posts' );
	} 

	// Capacidades del colaborador

	add_action( 'admin_init', 'modify_contributor_capabilities' );

	function modify_contributor_capabilities(){
	  global $wp_roles;
	  $wp_roles->add_cap('contributor','upload_files' );
	  $wp_roles->add_cap('contributor','edit_sonidos' );
	  $wp_roles->remove_cap('contributor','delete_sonidos' );
	  $wp_roles->remove_cap('contributor','edit_published_sonidos' );
	  $wp_roles->remove_cap('contributor','publish_sonidos' );
	  $wp_roles->remove_cap('contributor','edit_others_sonidos' );
	  $wp_roles->remove_cap('contributor','read' );
	  $wp_roles->remove_cap('contributor','delete_posts' );
	  $wp_roles->remove_cap('contributor','publish_posts' );
	  $wp_roles->remove_cap('contributor','edit_posts' );
	  $wp_roles->remove_cap('contributor','edit_users' );
	}

Thank you in advance!