WordPress 3.5 attachment_fields_to_edit and media_send_to_editor
So, there are some things which work differently (now). I. What you’ve noticed, when you click the checkbox WordPress sends an Ajax request to ‘wp_ajax_save_attachment_compat()’ with some form data, if your checkbox is checked, this information will be part of the form data. ‘wp_ajax_save_attachment_compat()’ checks for $_REQUEST[‘attachments’] and $_REQUEST[‘attachments’][$id] and will fail if it does … Read more