Novell GroupWise 8
A posted appointment is designed to be an appointment for the sender only. If at a later point in time, the sender wants to invite others to the appointment without recreating it from scratch, you can change it to a Group appointment. The sender's name, however, is not added to the To: field automatically so once the additional invitees are added and the appointment is sent, the original posted appointment is deleted from the sender's calendar, and therefore any mobile device they might be using.
At this time, the workaround is to remember to add the Sender's name to the To: field before sending the changed appointment. This has been reported to engineering asking that the behavior be changed to be the same as with a regular appointment where the sender's name is automatically added to the To: field