I just noticed you "can" sign in when you are already signed in with a valid user. For instance, if I have an active session with user John and I go to http://myhost/forum/people.php, it shows me the login screen, I log in with an existing, valid user (for instance, Peter/Peter) and it says me I am signed in and shows me the options to continue to discussions or to go to my account (the usual options when a user has successfully signed in). But instead, when I choose whatever option, the "signed in as" message shows me I'm still signed in with the previous user.
I guess Vanilla should do at least one of the following things when you are already logged in and try to log in with another user:
- Disable http://host/vanillapath/people.php and/or show a message saying "You are already logged in. Please log out first to log in with another user" if that is the case. - Or, if it doesn't say anything, at least if it lets the new user to log in, terminate the session with the existing user first.