@ray, i tested this again: enabled buddypress forum in the component setup, then reinstalled forum using existing bbpress installation setting ***.
I created a private group with forum enabled and posted a topic in this group forum. I then logout, used other browser to view the wpmu forum (bbpress), and I can still see the topic posted in the bppress that should have been a private post. When logged in as another user (non-group member), i can reply to that topic! That’s the privacy issue that I was talking abt.
*** would selecting new installation of bbpress overwrite my existing bbpress ?