WPMU user confusion

Hi Friends,

We recently switched over to a WPMU install (we are also running Buddypress), which was also once activated, and now activated again.

For our main site, we have many users available under Site Admin > Users, but any new users are placed under Network Admin > Users. I'm wondering if this is default behavior, or if something is causing this as it would seem logical to me they should be placed under the site in which they registered. I assume when WPMU was off, it would just go to the single install users section, but I assumed (perhaps falsely), that they would go to both network and site admin when WPMU was enabled.

Anyone know how it's supposed to work?