WordPress MU

In my MU installation everything works fine but whenever user chooses to create only a user in always create a user on the main blog which by default seems to have post permissions on all other blogs.
How can I make sure that each blog owner (lets say blog1.domain.tld) allows a new user creating for their own blog.
Whenever user goes to blog1.domain.tld/wp-signup it seems to redirect to domain.tld and the new user is created under domain.tld.

Is it possible to give each blog owner the possibility to have their own signup page?

Thanks