We are still trying to track how this is occurring but we have noticed that occasionally an appointment sent out through a proxied user weeks before hand will be sent and all will be fine till a few minutes before the appointment is due, then it will resend itself as if someone resent or rescheduled the appointment. We have only seen it 3 times so far but we have only been running 2012 SP1 for a couple of months now.

Anyone else seen this?

I know SP2 is out but I hate to jump on service packs to quickly.