Incorrect data after modifying post using backlink from wp_die

I have hook:

function myHook( $post_ID, $post )
{
    $data = get_post_meta($post_ID, 'data', true);
    if ($data)
    {
        _log('data:' . $data);
        /* here some checks and validation */
        if (!valid)
            wp_die('Error', 'Error',  array( 'response' => 500, 'back_link' => true ));
    }
    else 
        wp_die('Error', 'Error',  array( 'response' => 500, 'back_link' => true ));
}

add_action( 'save_post', 'myHook', 0, 2 );

Problem is that when data is incorrect and user uses back_link to correct data and tries to publish post again, his changes are not applied. Old data is taken into analysis. How can I fix this?

Thanks in advance