I spent few hours trying to understand how joomsef changes page title and honestly I still don't know... but what I know now is how to prevent such changes...

so - open /includes/joomla.php and replace every occurrences of $this->_head['title'] with something similar that joomsef won't find e.g. $this->_head['titl']

it workes fine for me and hope this tip will help you too ;-)