As I understand it, this improvement has not yet been fully tested and appears only in the bleeding edge version of BuddyPress. You should not use the bleeding edge version for production sites. According to the roadmap, the improvement will appear in 1.1 release of the stable version, due August 27th.

It is, certainly, a very welcome improvement - one of the best features of BuddyPress is the way in which it gives each group it's own forum, a very smart way to interweave the forum activity with the profiles and other social activities of the group members. This is so much smarter than having one monolithic forum section, with the forums all in one place, creating an artificial divide between the forums and the social elements of your site.

As such, bbPress is pretty much an essential part of BuddyPress but, until now, installing bbPress and then integrating it has been problematic, far more difficult than the MU side of things. I was lucky enough to find a good set of instructions and got my own site up and running fairly quickly, but I didn't bookmark the instructions and, when a friend tried setting up a BuddyPress site this week, he wasted several hours before giving up in frustration.

Anyone who encounters problems should consider waiting just a month for BuddyPress 1.1 but, if you have a use for it now, you might be as well try the current 1.0.3 version, you might encounter no problems, just search the BuddyPress.org developers forum for good instructions.