First: Thank you for your very detailed report, exactly what I need for bugfinding! I followed your guide up to this point:
Muad''Dib wrote:Checked the anonymous account. London was selected. Changed it.
Viewed the homepage. My account showed london also.
Went into ACP and changed my timezone.
Everything seemed great.
The anonymous account is not supposed to reflect the board settings immediately. The first time a visitor or bot will browse your board the time zone of ANONYMOUS will be changed to the board time setting (seems only logical to me, don't know why they are kept separate in the first place) - as you were browsing the board as an admin, the script never had the chance to change it. So this is not a bug.
Then I did as you did, I checked the setting for both my account and the board and both were at "America/Los_Angeles", not London. So I do not quite know what went wrong in your case... but seeing that it works fine now, I don't think it's severe.
If you really wanted to help me you could repeat all those steps from above and check if the same error happens again.