New User sees the main Blog under "My Sites"

Not sure if it's an BuddyPress-Issu.
When a new user registers (Membership) and adds a new Blog, he sees in his Backend not only his site, but also the main-site:
In the admin-bar, right next to the "W" where it says "my sites". Eventhough he sees pretty much nothing when he goes to the dashboard of the main site - but it would be nice if he doesnt sees it at all!
Or have activated something for the whole network again which I shouldn't?!