Safari shows saved usernames while 1Password is locked

In Safari, when I click a login box, my available usernames are shown even though 1password is locked. Only after I click one does it ask me to unlock 1password. So the password is protected, but the usernames are exposed.

Obviously fine most of the time, but some people on some websites might not want all their secret aliases to pop up when a guest is borrowing their computer! In fact, on some sites it could be a problem to just reveal the fact that I have an account at all. 

Have I got a setting wrong somewhere?