Change Recepient in a reccuring Appointment

Hi

We have installed the newest GroupWise 2012 SP2 on ORS2SP3 and the Client on Windows 7 64bit. The language of the GroupWise Client is German.
I want to add an recepient only on one day of the recurring Appointment

Steps to reproduce:
- Send an reccurring an appointment to a few Users
- Modify one of Appointment, GroupWise asks to edit all or only a single message-> i chose a single message
- Add an additional recepient and click send

The recepient is added to all messages, not only the one i selected.
Is this a bug?

Thank you for your answer.