In SOGo Webinterface:
When planning a new event and inviting attendees, the free/busy time differs from the calendar.
Even with my very own calender, the events are shifted between 1 hr to 23 hrs.
E.g. web calendar event on 04/03/13 10 - 11 am shows up in the "invite attendee free/busy" view at 04/04/13 09-10 am.
Behaviour seems to be different in differeetn weeks, sometimes no shift, sometimes 1 hr, sometimes 23 hrs. | 
