Multi site cross login fail

Hello everyone

Sorry if my english is wrong, i’m a french user 🙂

I’ve got some probleme with wordpress 3.0.4 and secure system, i explain :

I’ve got N “subsites” a a wordpress, subdomain configuration

http://user1.mysite.com with user1 account
http://user2.mysite.com with user2 account
http://user3.mysite.com with user3 account
…

If i auth user1 on
http://user1.mysite.com/wp-admin/ with user1 account, then go to
http://user2.mysite.com/wp-admin/, i’m on the user2 site administration.

I don’t want user1 to access user N admin.

Does someone have the same problem ?
How can i fix it ?

Thanks a lot everyone.

Raffiki