The filled in form with the old OTP when accessing the forum is caused by your browser which is saving the form input. You can disable this behavior in the options of your browser. I don't know if the lastpass plugin in may be cause this issue as well (as i am not a lastpass user)
Regarding LastPass, once you have authenticated you wont need to re-authenticate for every login. This would make the user experience an incredible pain.
If you are being prompted for authentication only when you open your passwords' database first time that is an expected behavior.
However you may want to look into LastPass options or contact lastpass support for more information about its functionalists at
support@lastpass.com