Using IE, she logs in does what she needs to do then closes her browser window. When she opens another browser window, it prompts for a log in and when she tries to log in it says she's already logged in.
I have been able to replicate the behavior in IE7. I log in, close the browser window, open a new one, and I'm still in the "_loggedin" table, but IE doesn't have the active session any longer, so I can't log in.
For the time being I've asked her to use the log out function instead of closing the window.
EDIT: It also does this with Firefox, so it's not an IE issue.
EDIT2: OK, I'm reverting to pre-1.2.0 because I've now gotten 6 complaints since upgrading. That's a shame. I really like the user tracking system.
