SchedulingPlugin does not respect RFC 6638 3.2.8.

[georgehrke]

Spec: https://tools.ietf.org/html/rfc6638#section-3.2.8

A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE",
"RRULE", "RDATE", or "EXDATE" property changes in a calendar
component such that existing recurrence instances are impacted by the
changes, as shown in the table below. Servers MUST reset the
"PARTSTAT" property parameter value of all "ATTENDEE" properties,
except the one that corresponds to the "Organizer", to "NEEDS-ACTION"
for each calendar component change that causes any instance to be
rescheduled.

Related code:

dav/lib/CalDAV/Schedule/Plugin.php

Line 636 in d5a184c

if ($attendee->getNormalizedValue() === $message->recipient) {

It does not reset the participation status to NEEDS-ACTION, if $message->significantChange is true.

Edit:
https://github.com/sabre-io/vobject/blob/master/lib/ITip/Broker.php#L69 does not fully overlap with the properties listed in section 3.2.8. Needs a new property in Sabre/VObject's ITIP/Message.

[DeepDiver1975]

Hey @georgehrke 👋 - thanks for the report. Will you submit a PR? Much appreciated ....