E-Commerce order tracked with wrong user (no replies)

I've semi-successfully implemented the e-commerce tracking. The only problem I still have is that the actual order that's being tracked is not being assigned to the right user. It always ends up creating a new visitor ID, so the actions that lead to the actual purchase are never linked to it.

I do all the tracking in JS except for the addEcommerceItem() and doTrackEcommerceOrder() calls. They are run on the PHP side, using the class provided by you handsome people.

I've already tried manually setting

 $tracker->setIp( $_SERVER["REMOTE_ADDR"] ); 

before any of the calls mentioned above, but that didn't help either. So how can I fix that?