I am also experiencing strange time zone issues.
I configured all users to use AEST (ie: a timezone of (GMT+10.00) Canberra / Melbourne / Sydney).
However, it seem that the users who use the system remotely have had their timezones changed - 3 have been reset to (GMT-08.00) Pacific Time (US & Canada) / Tijuana presumably because their home PCs have not been configured for a timezone of AEST.
Another user is on holiday in Italy and his timezone has ben set to (GMT+01.00) Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna.
I am using the following command to check their TZ setting:
and using this command to reset it:
zmprov ga username | sed -n 's/^zimbraPrefTimeZoneId: //p'
Zimbra version is 3.1.1_GA_394.
zmprov ma username zimbraPrefTimeZoneId "(GMT+10.00) Canberra / Melbourne / Sydney"
Hope this helps - Angus