in "libraries\plugins\AuthenticationPlugin.php", line 96:
session_unset(); session_destroy();
I think it's better that you manually unset the parameters that needs to be deleted, instead deleting the whole session. I am having much problems, because PMA destroys all my other sessions too.
(btw, it is nicely done like in: "libraries\sessions.inc.php" , line 26, where it checks if session exists, it just closes);