It could be argued this is a feature, it may also essential if the authorisation comes from elsewhere (logins/password)
You could look into startup actions to set a user name each time. You need to set the text of
$:/status/UserName
We no longer use cookies as we did in TWC to do this.
I have being working on a Login process that remembers user IDs for selection in a tiddler tagged $:/tags/StartupAction but its not ready for publication and version 5.1.18 has quite a few changes coming in this regard.
Tony