Your name may appear as logged in twice if you open 2 browsers and log in in both of them, or if you have two computers and log into the site from both of those at the same time. Also, there is a brief period of time after you close your browser window (unless you click "log out") before the server automatically removes your name for lack of inactivity. If you log in from another computer or browser during this time your name will appear twice. Its nothing to worry about and poses no security issues or confusion on the back end.