Codeigniter AR and JOIN() with brackets?

[eluser]_jon[/eluser]
I have a bunch of code that used to work in CI 1.6 but since the update, it has ceased to work. It appears that the brackets in this piece of code are being trimmed out:

Code:

$this->db->join('subscriptions', '(subscriptions.subscription_user_id = ' . $this->user->getId() . ' and subscriptions.subscription_thread_id = threads.thread_id)', 'left');

Is there any way I can stop this happening? I don't want to edit the base CI classes if at all possible... it's causing my queries to fail currently!
Thanks.