[Plugin: Meta Box] meta box Select type with 'multiple' decleration doesn't saves al

i’m using metabox 4.1.11.
when i’m registering this meta-box:

$meta_boxes[] = array(
	'id' => 'projects',
	'title' => 'Pin to project',
	'pages' => array( 'post', 'event', 'designs', 'links' ,'images' ,'files' , 'videos' ),
	'context' => 'side',
	'priority' => 'low',
	// List of meta fields
	'fields' => array(
		array(
			'name'		=> 'project to pin',
			'id'		=> "per-projects",
			'type'		=> 'select',
			'multiple'	=> true,
			'options' => array(
				'project 1'		=> 'project 1',
				'project 2'		=> 'project 2',
				'project 3'		=> 'project 3',
				'project 4'		=> 'project 4'
			)
		)
	)
);

http://wordpress.org/extend/plugins/meta-box/