I have changed the IP of one Post Office. (Created a new cluster resource
for this PO, which was together with another PO on one cluster resource

Everything works for this PO, but CalDAV only works unidirectional: if I
change an appointment in the external program this change is successfully
synchronized to GroupWise. But the other way does not work. Only when I
restart gwcalsrv the items are updated, but only one time, subsequent
changes are again ignored.

The problem only exists for existing users, for a newly created user
synchronization works both directions.

Is there some sort of cache somewhere, something that might prevent calsvr
to recognize items from the changed PO?