When one of our users accepts a meeting it is 1 hour ahead, but nothing is patched. Why is this?

Q: Following the patch on Exchange 2003, we have a user who has booked a meeting with multiple users March 14. When they accept, the meeting time is changed 1 hour ahead. No patches have been applied to the desktops or the BlackBerry server yet. Help!
A: There are a lot of moving parts here. The view of the meeting is always interpreted in light of the OS time zone rules in effect on the CLIENT at the time.