@cyberzork Thank you very much for your investigations.
I think it is not a common use case, that I invite my collegues to a personal event (event for my hairdresser or swimming with my kids 
) only to show the events in their calendar.
But I want to show them that I’m busy at that time.
I don’t think that the current implementation of private event is a bug, but we should consider to add a feature request to support events that should private and are shown in shared calendars.
@cyberzork Do you know, how to add some kind of feature request?