CRM_Core_BAO_CustomGroup::getTree() returns the same tree, no matter what are the params

We call CRM_Core_BAO_CustomGroup::getTree() from CRM/Contact/Form/Merge.php to obtain the custom data hierarchy and values → labels mappings for a contact. Unfortunately, on current trunk, this function returns the same tree, no matter what contact_id is in its call.

To reproduce: Create two contacts with different values for a given custom data field. Call this function with these two contact_ids - the returned trees will carry the same values for both contacts.