WordPress MU

well , i'm into a real problem now
i'm testing WPMU on a not working / not critical site, i opened the registration for testing some stuff on the registration page then when i logged in i found there're nearly 8 users added to the main blog !!!!
i really don't know what happened nor how they did it
i wish that's something can be solved or anyone here has faced the same problem and came over it
i'm using 1.5.1 version
thanks in advance

Users without blogs get added to the main blog as subscribers so that they have a place they can change their password, etc.

Standard behavior, has been for quite a while.

thanks lunabyte

so it's a normal behavior ?
just i thought users signed up for just usernames don't get access or added to another blog till the user/admin add them to it

Standard behavior, has been for quite a while.

thanks lunabyte for your help