kcalcore uses schedulingId to determine the connection between an invitation and an event. This is not RFC conform, and breaks the handling with other clients, if the calendar is shared, like with rcm and wallace. That's why kontact should not use the schedulingId anymore.

More specifically, the scheduling id is used to identify the specific instance of an event in a folder/calendar that was used in an invitation. This helps to update the correct copy in case of the same event being in multiple folders (some of which may be shared folders from other users).