I know this software is not being developed any longer, but maybe someone has found a workaround for this.
The thing is that if an appointment created by CalSync is dismissed by Thunderbird (accessing Google Calendar via 'Provider for Google Calendar 0.9" addon), then CalSync recreates the appointment in Google Calendar, originating a duplicate on next sync.
I think the origin of the problem is that somehow CalSync is no longer able to identify the dismissed event as an event that it has created. For CalSync the event no longer exists in Google Calendar, so it creates it.
Asking the developer to change the code is not an option, but could you explain how CalSync detects if an event in Google Calendar has been created by it or if is a Google Calendar "native" event?
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