I believe this issue is related to the Funambol client, not with Group Office sync process, but it is hard to be sure. Please read and post back if you can generate this issue, or if you know of a fix, or an alternative way to sync a Group Office user's Calendar with their Exchange account's Calendar.
We have the issue that within both Outlook and in Group Office, reoccurring appointments are changing the day from which they are set to, to the day before the appointment was first created. Not every reoccurring appointment shifts backward by one day, but >75% of the time they will.
That is if you create a reoccurring appointment for a Friday, then at some time in the future it will move to the Thursday. If it was created on the Monday, it will move the the Sunday. This appears to be only happening for reoccurring appointments, other types of appointments do not shift.
I have replicated this issue via Outlook, "New Reoccurring Appointment", accepted the default "Start:" time of "8:00 AM" and "Duration:" of "30 minutes", then selected a four day "Range of recurrence" by selecting an end date. It does not seem to mater if there is an end date or "No end date" the appointment can still shift.
Once I created an appointment and it shifted just as I saved it, so I checked the Funambol Sync Client and it was not due to sync for another 5 minutes, so I started to wonder if the issue is independent to the sync process, but just something about the Funambol Client running. Maybe I made a mistake during creating this test?
It is my believe that once the appointment date is corrected, then it will not change dates again, and that if the date has not shifted in the first day (maybe in the first hour) then the date will never shift.
I have checked Time Zones, etc, of the PC and the Group Office server and all is on the same time zone and is set correctly.
I upgraded the Funambol client to the latest (which was at the time of testing: 10.0.6, "Funambol Windows Sync Client"), and our Group Office Professional is Version: 3.7.29.
Sadly this has so greatly impacted our use of the Funambol client that we have had to cease using it . Having correct dates in Calendar's is very important.
Example of a reoccurring appointment in Outlook;
Recurrence: Occurs every Friday effective 18/02/2012 until 22/04/2012 from 8:00 AM to 8:30 AM.