Problem with clonable group?

Hi,

i would ask, if there is a bug with clonable group on setting page. Here is sample code:

With this code, on admin site i get only one input (type "text" with id "mb_top_posts") - so not textarea, no checkbox field.

$prefix = 'mb_';

$meta_boxes[] = array(
		
		'id' => 'top_i',
		'title' => ' ',
		'settings_pages' => 'top-positions',
		'tab' => 'position_i',

		'fields' => array(
			array(
				'id' => "{$prefix}top_posts",
				'type' => 'group',
				'clone' => true,
				'fields' => array(
					array(
						'name' => __('Perex','textdomain'),
						'id' => "{$prefix}perex",
						'type' => 'textarea'
					),
                                       array(
						'name' => __('Hide',TEXTDOMAIN),
						'id' => "{$prefix}hide",
						'type' => 'checkbox'
					),
				)
			)
		)

	);

(WP 4.7.5, latest metabox plugin and addons)