I'm running Zimbra 6.0.5 Network. I just upgraded Mac OS X from 10.6.3 to 10.6.4. Using Zimbra Connector 6.0.2423.
After upgrading to 10.6.4 I opened iCal. My Connector is set to sync every minute. At the time of each sync, a new Zimbra CalDAV account would be created. I reinstalled the Connector and the behavior still manifests.
I am trying to track down some relevant log messages.