iCal auto sent out an past event ( attendee @ this past event ) as Organizer

Recently my colleague facing an issue that her calendar auto send out an past event that she attended.

13 Nov 2017 - Vendor ( Using google calendar ) as an organizer sent out an invitation. My colleagues as attendee. Accepted on 13 Nov 2017.

14 Nov 2017 - I re-sync my colleague iCal and it auto send out the same event to whole list of attendees @ that event as an organizer "Automatically", which she was an attendee on 13 Nov 2017

Can you explain how it would be happen ? Is that a bug issue for iCal , because my colleague using Microsoft outlook mail , and she using iCal & the origin event organizer using Google Calendar.

Thanks.