I am having an odd problem with one user on our system. He has multiple calendars (say "Calendar", "Tentative" and "Personal") that he syncs via CalDAV to iCal (v5.0.1, Mac OS 10.7.2). He and his assistant will also use the web client to access the calendar.

The problem is that if an event is deleted from "Calendar" in the web client, the change does not properly sync to iCal. An event added in the web client will sync. An event deleted from "Tentative" or "Personal" in the web client will sync as well. All changes made in iCal seem to sync back just fine to the server and are reflected in the web client.

My troubleshooting so far has been to make sure this isn't a corruption of his local iCal files. The exact same problem persists if iCal is setup in a completely fresh account on a different system. The initial sync of the calendar is good, reflecting all that is seen in the web interface, but fails to reflect subsequent deletions only from the "Calendar" calendar.

No other users have a similar problem, so I am guessing that this is an issue specifically related to some content of this particular "Calendar" calendar. Where should I be looking, on both the client and server sides, to further troubleshoot this?