Another FormBuilder question

I've just been reworking some of the formbuilder code I was working on and asking questions about a couple of weeks ago and have run into a problem. I know I've encountered it before, but I can't remember how I got around it, which has been driving me crazy... I'm using the same function to build my form whether it's for editing a user or creating a new one. My code looks like (with relevant input validation elsewhere): $data = DB_DataObject::factory('users'); if (!empty($_GET['id'])) { // I've tested and this is only happening when it ought to be $data->get($_GET['id']); } $ebuild =& DB_DataObject_FormBuilder::create($data); $form = $ebuild->getForm(); if ($form->validate()) { $form->process(array(&$ebuild,'processForm'), false); return; } // Go on to output form and so on. The error I'm seeing is that when I create a new user the DataObject tries to insert it using an UPDATE query. ie: dataobjects_users: QUERY: UPDATE users SET user_name = 'James Stewart' , etc, etc, etc WHERE users.user_id = IS NULL Obviously this isn't working, but I can't remember why it's using UPDATE instead of INSERT in this instance. thanks. James.