The problem lies in the tabbed-login.php file. There on line 61 is:
$current_url='http'.(empty($_SERVER['HTTPS'])?'':'s').'://'.$_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI'];
It assumes that when your site is not running on SSL, the “HTTPS” server variable is EMPTY. But it is not: My server says: “off”. And so it thinks:.. ok.. not empty.. you are using SSL then..
SO: I changed the line to:
$current_url='http'.($_SERVER['HTTPS']=="on"?'':'s').'://'.$_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI'];