Outlook appoinment date changes when opened by some recipients.

[Katy]

We have about 5 users who are experiencing the same issue - they receive an
appointment request from an external (outside our domain) sender but when
they open or view the appointment, the time and date change to approx 1/2 an
hour in the future (goes to next 1/2 hr slot). eg. User is sent an
appointment for 4:15pm on Friday 5th August 05. They receive and view the
appointment request at 1:50pm on Wednesday 3rd August 05 - the appointment
time immediately changes to 2pm, Wed 3rd August 05 (even before they accept
it). When the user does accept the appointment, it shows up in their
calendar as the new (incorrect) time. Both the sender and the recipient are
in the same time zone & country, and the appointment still shows correctly
for the sender and other recipients. The only common factor between the 5
users affected is that they have recently travelled outside of the country.
While travelling, the time zone remained the same on their laptops, but
changed to the local time zone on their mobile phone. Each user
synchronised their phone calendar/diary with their Outlook calendar (on the
laptop) while travelling (eg. while the phone was set to a different time
zone). This issue has only started occuring since they returned from their
travel.

Both the laptop and the mobile phone are now in the same time zone/country
and this is only occurring on the laptop they travelled with. The software
on the laptops is Windows XP (SP2), with Office 2003.

Any ideas on what could be causing this issue or how to fix it?

Thanks,
Katy.