Select Advanced multiple does not return an array

When I create a metabox

'fields' => array(
	array(
	'id' => 'related_products',
	'type' => 'post',
	'name' => 'Related product',
	'post_type' => 'product',
	'field_type' => 'select_advanced',
	'multiple' => true,
	'select_all_none' => true,
),

and display the result

$values = rwmb_meta( 'related_products');
echo $values; 

then I get the ID of only the first post, not the array.

Accordingly, the code:

$values = rwmb_meta( $field_id );
foreach ( $values as $value ) {
    echo $value;
}

produces an error:
Warning: Invalid argument supplied for foreach() in

Is this a bug in the plugin or am I doing it wrong?

if i do clone instead of multiple :

'field_type' => 'select_advanced',
'clone' => 1,
'sort_clone' => 1,

then everything is fine, I get an array.

PS. Sorry for my english.