Updating Meeting causes new Creation of Meeting

Hello there,

I've got a strange problem in EWS Exchange Developtment ( c# )

Everytime i try to Update an appointment i've just created exchange creates another appointment.

Does anyone know why this happens?

All i do is changing the room resource of the appointment.

Here is the Code for creating the Item:

            ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP2);
            service.Credentials = new NetworkCredential(serviceAccount, servicePasswort); 
 service.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, mail);
            service.Url = new Uri(exchangeWebService);
            Appointment raumbuchung = new Appointment(service);
            raumbuchung.Subject = betreff;
            raumbuchung.Body = buchung.Beschreibung;
            raumbuchung.Body.BodyType = BodyType.HTML;
            raumbuchung.Start = Start;
            raumbuchung.End = End;
            raumbuchung.Location =room;
            raumbuchung.AllowNewTimeProposal = false;
          raumbuchung.RequiredAttendees.Add(email);
            raumbuchung.Resources.Add(roomAdress);
            raumbuchung.Save(SendInvitationsMode.SendToAllAndSaveCopy);
            return raumbuchung.Id.UniqueId;

and the Codeblock for updating:

    ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP2);
            service.Credentials = new NetworkCredential(serviceAccount, servicePasswort);
            service.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, mail);
            service.Url = new Uri(exchangeWebService);
            Appointment raumbuchung = Appointment.Bind(service, new ItemId(TerminID));
            raumbuchung.Subject = betreff;
            raumbuchung.Body = beschreibung;
            raumbuchung.Body.BodyType = BodyType.HTML;
            raumbuchung.Start = start;
            raumbuchung.End = end;
            raumbuchung.Location = newRoom;
            raumbuchung.AllowNewTimeProposal = false;
            raumbuchung.IsResponseRequested = false;
            raumbuchung.Update(ConflictResolutionMode.AlwaysOverwrite);

            return raumbuchung.Id.UniqueId;

Is there anything wrong? One thing I recognized is when the appointment got an update it changes the UniqueId.