How Do I set no redirect? I am getting a weird scrollbox on my pages

I have a multipage form at the end of which I want the user to click a link in the page which pops up a thickbox user/login form which the user fills out, it closes, and comes back to where they were - the final part of the form, where they can then click the submit form button and the form gets submitted with their user id attached.

I have this almost working - you can go through the form, click the logon link, get a thickbox login form, fill it out - BUT when you hit "log on" it takes you ?q=user/login&destination= pages, not just closing the thickbox and being on the same page you clicked the link on.

In my FAPI module I have

function mymodule_form_alter(&$form, $form_state, $form_id) {
switch ($form_id) {
	case 'user_login':
	$form['#redirect'] = FALSE;
	 break;
    }
}

which didn't work

So I enabled disable redirect for user login and that didn't work either. It took me to ?q=user/login&destination= but with a tiny scrollbox with the following in it

{ "status": true, "updaters": [  ], "debug": [  ], "messages_error": [  ], "messages_status": [  ], "messages_warning": [  ], "redirect": "http://opal-dev.test.www.nhm.ac.uk/?526493836=1", "preview": null, "form_id": "user_login", "options": { "enabled": true, "disable_redirect": true, "remove_form": false} }

Any suggestions?
Thanks. So close yet so far...
Katherine