Why does new user still use GMT time zone even though the default is set otherwise

[joehuang]

Hi,

I set a different time zone (e.g. GMT+8) in admincp -> options -> default time zone offset

And the remark for this setting says

"This is the default time zone for guests and new members on your forum"

After the setting, the guests can see the time zone change. However, when I register a new member, the default time zone for this new member is always GMT instead of the timezone I set in the admin option.

Anybody could help? This is a newly-installed vBulletin 4.2.0.

Thanks.
Joe