Facebook Connect

When using the Facebook Connect the UNA platforms sends new users a "temporary password."   If the user signed up using FB Connect the user can continue to sign on this way and has no need for a temporary password  and yet this email cannot be disabled.  What is the point of the PW and why can't it be disabled.  It creates a lot of confusion for new users.  I've joined dozens of membership sites using a FB connect and haven't been mailed temp passwords.