Hmm, I have not seen this, but I did find something on it. From the software setup guide:
During CIFS setup, you are prompted for the root password. When you enter the current password, it is not accepted. If you want to continue using the same password, you can enter Ctrl-C to stop the setup script and set the password history to 0. If you want to use a different root password, you can change the password at the prompt. If you modify the password history to 0 to use the existing password, you need to reset it to the old value after completing CIFS setup.
Check "option security". security.passwd.rules.history looks like it started defaulting to 6 in 8.0, and is enforced if security.passwd.rules.enable is on, which is also the default in 8.0. Try disabling the rules or setting the history to 0, then try again.
Bill