The Changelog entry:

2013-11-25	Jan Tatarik	 <jan.tatarik@gmail.com>

	* gnus-icalendar.el (gnus-icalendar-event-from-ical)
	(gnus-icalendar-event->org-entry)
	(gnus-icalendar--update-org-event)
	(gnus-icalendar-event->gnus-calendar): Distinguish between
	required/optional/non-participant attendee status. Fix bug causing
	the first required event participant to be omitted.