I have a user with Mac OS 10.5 and we are using iSync 5.0.2 and all of the latest apple patches have been installed.
When you go to delete an entry from ical it reappears moments later when the sync finishes. The only way to delete a calendar entry is to delete it from the Zimbra web interface and then delete it from ical before a sync happens. Then the entry remains deleted.
If you modify an entry then you end up with the original unmodified entry and the modified entry once the sync is compete.
I have tried a reset of sync data and also uninstalling (as best as you can) the isync connector and then reinstalling it.
Any help would be greatly appreciated. Thanks!