I'm experiencing the same issue with our Zimbra-based calendars. Some events -- seemingly only invitations sent to me (and received via Zimbra) by Outlook users -- have exactly the same duration of 49,710 days, 3 hours, and 28 minutes (which is 4,294,956,480 seconds, or 71,582,608 minutes, or 1,193,043 hours).
This CANNOT be coincidence. There's clearly a repeatable bug here.
To verify this, put your meeting start and end dates and times into this page --
Time Duration Calculator: Time between two dates/times -- and it'll figure it out for you automagically.
We haven't been able to diagnose this yet, but it's making the use of CalDAV very unattractive right now.
Meanwhile, Google calendars are CalDAV'ing beautifully. Love the live updates!