[Koha-devel] Blocking an account

Hi I'm trying to figure out how to block a user account so that he cannot borrow books. I've found a flag labeled "Borrow books" in Koha 1.9.3 but unticking it and applying doesn't seem to block the account : using the librarian account (super user) I still can borrow books for the specified user without any warning or message telling that the user cannot borrow books. Am I doing something wrong or should I report a bug ? Thanks Jerome