I have a single user on our system using Zimbra Desktop version 1.0.3 build 1691 connecting to my Release 6.0.0_GA_1802.UBUNTU8 UBUNTU8 FOSS edition server and they are seeing an incorrect time zone when they reply to a message. The standard reply shows the original message including the sent time which shows as this.
Sent: Thursday, October 22, 2009 4:14:18 PM GMT -06:00 Guadalajara / Mexico City / Monterrey
instead of the correct time zone of GMT -06:00 Central Time US/Canada.

So far I have confirmed the time zone settings in windows (XP SP3) are correct, the preferences within Zimbra desktop are correct, the settings on the web client are correct and finally the COS settings are correct as well.

When the user sends emails using the web client the date / time stamp are correct (granted they don't show the time zone at all). No other user has this problem.

Is there any way to fix this issue?

Can I edit the reply settings from somewhere to remove the time zone information?

Any advice would be appreciated.