Currently, when you are logged in, you can still veiw the login screen ( http://cotonti.com/users.php?m=auth ). This should be changed and made so that you get an error message ("You are already logged in! Redirecting...) and it redirects you to the homepage (or some other page like that).
It should not log you off though, if you logged with "Remember me". It should just say something like "Your session has expired, try again" and show you the form with the text you have previously entered.
on some occasions I damned cotonti for expiring my sessions whilst typing long posts.. Never, ever saw that warning you've posted.. Lost all text.. Now I type it localy and copy/past it.. (upside is that I do not have to damn cotonti anymore :p)