We use Exchange 2010 with Outlook 2010 (both incl. SP1) in our company and actually have a strange behavior with appointments:
An appointment arrives from an external mail system. Appointment starts at 2 pm. The appointment is neither accepted nor declined. After a few minutes an update arrives, scheduling the appointment to 4pm. When this appointment is now accepted, Outlook enters the appointment at 2 pm. When you open the details of the appointment mail, you see the correct time starting from 4pm, so the update mail seems to be processed.
Any suggestions on that?