We're using cURL to send .ics formatted files to add and modify events in our users Zimbra (5.0.20) calendars. It all seems to work OK as long as we don't cancel an event and then try to add/modify it again using the same event UID. If we try to reuse the UID, we get an 'HTTP ERROR 500, system failure: ics formatter failure' response.

Is this normal behavior? If so, is there a way (hopefully programmatic) to clear the UID from Zimbra so that it can be reused? If not, any idea how to fix it?