We've seen this issue randomly and multiple times and on the last couple mobility builds.

"When an appointment with multiple recipients is accepted on an iPad the appointment is duplicated and sent as a new appointment to all of the original recipients with the iPad user as the new sender. The appointment the iPad user originally received is deleted and only the appointment they generated remains.

The other recipients retain the original appointment and are presented with a duplicated appointment coming from the iPad user to accept/decline. Post office and mobility logs show the activity, but do not reveal the source of the new duplicated appointment sent on behalf of the iPad user. This has occurred on multiple mobility servers and with users on different post offices."

GW 8 SP2 HP2
Mobility Build 428
iOS 4.3.3