[Ietf-calsify] Include scheduling data in ITIP VEVENT REPLY?

[Caleb Richardson]

Is is required to include the original scheduling data (DTSTART 
property, DTEND property, VTIMEZONE component, DURATION property) when 
sending an ITIP REPLY for a VEVENT?

RFC 2446 section 3.2.3:

The optional properties listed in the table below (those listed as "0+" 
or "0 or 1") MUST NOT be changed from those of the original request.  If 
property changes are desired the COUNTER message must be used.

RFC 2446 section 4.2.2

    BEGIN:VCALENDAR
    PRODID:-//ACME/DesktopCalendar//EN
    METHOD:REPLY
    VERSION:2.0
    BEGIN:VEVENT
    ATTENDEE;PARTSTAT=ACCEPTED:Mailto:B at example.com
    ORGANIZER:MAILTO:A at example.com
    UID:calsrv.example.com-873970198738777 at example.com
    SEQUENCE:0
    REQUEST-STATUS:2.0;Success
    DTSTAMP:19970612T190000Z
    END:VEVENT
    END:VCALENDAR

So this seems to indicate that no, scheduling data is not required to be 
included. However in my interoperability testing I have found that 
Google Calendar requires scheduling data to be present.

What is the purpose of including VEVENT scheduling data in a REPLY? Why 
does the spec even indicate it as optional? Is Google correct in their 
requirement?

Thanks,

Caleb Richardson
caleb at everyone.net