Custom metabox with image gallery upload that won’t attach images to post

I have created a custom metabox with an image uploader that will upload multiple images into a gallery that I can then query. It all works accept for the fact that the images don’t show as attached to the post in the media library. They are showing as unattached. Any ideas folks?

<?php
// Add the Meta Box
function agch_properties_add_custom_meta_box() {
    add_meta_box(
        'custom_meta_box', // $id
        'Property Photos', // $title
        'agch_properties_show_custom_meta_box', // $callback
        'properties', // $page
        'normal', // $context
        'high'); // $priority
}
add_action('add_meta_boxes', 'agch_properties_add_custom_meta_box');

// Field Array
$prefix = 'agch_properties_';
$custom_meta_fields = array(
    array(
        'label'=> 'Upload Images',
        'desc'  => 'This is the gallery images on the single item page.',
        'id'    => $prefix.'gallery',
        'type'  => 'gallery'
    ),
);

// The Callback
function agch_properties_show_custom_meta_box($object) {
        global $custom_meta_fields, $post;
        // Use nonce for verification
        echo '<input type="hidden" name="custom_meta_box_nonce" value="'.wp_create_nonce(basename(__FILE__)).'" />';

        // Begin the field table and loop
        echo '<table class="form-table">';
        foreach ($custom_meta_fields as $field) {
                // get value of this field if it exists for this post
                $meta = get_post_meta($post->ID, $field['id'], true);
                // begin a table row with
                echo '<tr>
                <th><label for="'.$field['id'].'">'.$field['label'].'</label></th>
                <td>';
                switch($field['type']) {
                        case 'gallery':
                        $meta_html = null;
                        if ($meta) {
                                $meta_html .= '<ul class="agch_properties_gallery_list">';
                                $meta_array = explode(',', $meta);
                                foreach ($meta_array as $meta_gall_item) {
                                        $meta_html .= '<li><div class="agch_properties_gallery_container"><span class="agch_properties_gallery_close"><img id="' . esc_attr($meta_gall_item) . '" src="' . wp_get_attachment_thumb_url($meta_gall_item) . '"></span></div></li>';
                                }
                                $meta_html .= '</ul>';
                        }
                        echo '<input id="agch_properties_gallery" type="hidden" name="agch_properties_gallery" value="' . esc_attr($meta) . '" />
                        <span id="agch_properties_gallery_src">' . $meta_html . '</span>
                        <div class="agch_gallery_button_container"><input id="agch_properties_gallery_button" type="button" value="Add Images" /></div>';
                        break;
                } //end switch
                echo '</td></tr>';
        } // end foreach
        echo '</table>'; // end table
}

// Save the Data
function agch_properties_save_custom_meta($post_id) {
        global $custom_meta_fields;
        // Verify nonce
        if ($_POST && !wp_verify_nonce($_POST['custom_meta_box_nonce'], basename(__FILE__)))
                return $post_id;
        // Check autosave
        if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE)
                return $post_id;
        // Check permissions
        if ('properties' == get_post_type()) {
                if (!current_user_can('edit_page', $post_id))
                        return $post_id;
        } elseif (!current_user_can('edit_post', $post_id)) {
                return $post_id;
        }
        // Loop through meta fields
        foreach ($custom_meta_fields as $field) {
                $new_meta_value = esc_attr($_POST[$field['id']]);
        $meta_key = $field['id'];
                $meta_value = get_post_meta( $post_id, $meta_key, true );
                // If theres a new meta value and the existing meta value is empty
                if ( $new_meta_value && $meta_value == null ) {
                        add_post_meta( $post_id, $meta_key, $new_meta_value, true );
                // If theres a new meta value and the existing meta value is different
                } elseif ( $new_meta_value && $new_meta_value != $meta_value ) {
                        update_post_meta( $post_id, $meta_key, $new_meta_value );
                } elseif ( $new_meta_value == null && $meta_value ) {
                        delete_post_meta( $post_id, $meta_key, $meta_value );
                }
        }
}
add_action('save_post', 'agch_properties_save_custom_meta');

function AGCH_properties_load_wp_admin_style() {
        wp_enqueue_media();
        wp_enqueue_script('media-upload');
        wp_enqueue_style( 'AGCH_properties_admin_css', get_template_directory_uri() . '/library/css/properties_gallery_admin.css' );
        wp_enqueue_script( 'AGCH_properties_admin_script', get_template_directory_uri() . '/library/js/properties_gallery_admin.js' );
}
add_action( 'admin_enqueue_scripts', 'AGCH_properties_load_wp_admin_style' );
?>