Multiple Selecet field values are not saved

Yes,

The strange thing is that it works for posts post type but not for the attachment post type. This is it:

		$meta_boxes[] = array(
		'title' => esc_html__( 'Artist Info', 'colours-of-a-journey-plugin' ),
		'post_types'  => 'attachment',
		'media_modal' => true,
		'fields' => array(
			array(
				'name'		=> esc_html__( 'Theme tags (select one or more values)', 'colours-of-a-journey-plugin' ),
				'id'		=> $prefix . 'attachment_theme_tags',
				'type'		=> 'select',
				'options'	=> array(
					'past'		=> esc_html__( 'Past', 'colours-of-a-journey-plugin' ),
					'present'	=> esc_html__( 'Present', 'colours-of-a-journey-plugin' ),
					'future'	=> esc_html__( 'Future', 'colours-of-a-journey-plugin' ),
					'home'		=> esc_html__( 'Home', 'colours-of-a-journey-plugin' ),
					'nature'	=> esc_html__( 'Nature', 'colours-of-a-journey-plugin' ),
					'passage'	=> esc_html__( 'Passage', 'colours-of-a-journey-plugin' ),
					'peace'		=> esc_html__( 'Peace', 'colours-of-a-journey-plugin' ),
				),
				'multiple'			=> true,
				'select_all_none'	=> true,
			),
		),
	);