Quick Addition...I found this in the logs...
40373] (05/08 10:03:08.842):{0x12E0} {John@xxxxx} Queuing notification of modified appointment (external). EntryId=89533 (delay processing 2 seconds)
[40373] (05/08 10:03:08.858):{0x12E0} {John@xxxxx} Queuing notification of modified appointment (external). EntryId=89534 (delay processing 2 seconds)
[40487] (05/08 10:03:08.858):{0x1E80} {John@xxxxx} Not requeuing calendar item EntryId=89534 - same source key as DuplicateEntryId=89533
[30000] (05/08 10:03:10.876):{0x1440} {John@xxxxx}-DoCalendarPacketProcessing-Tag=89533 Send calendar optimization packet to device
[40000] (05/08 10:03:10.876):{0x1440} {Johnxxxxx}-GetAndCheckProperties- Returned Property PR_START_DATETIME is invalid, PR_SOURCE_KEY is F4196391640E3646BDD2952C2453C20000000021DD61
[40000] (05/08 10:03:10.876):{0x1440} {John@bnbiz.org}-GetRIMCalendar- GetAndCheckProperties failed Entry tag =89533
[40000] (05/08 10:03:10.876):{0x1440} {John@xxxxx}-CalendarPacketProcessOptimization- GetRIMCalendar() failed error=1 EntryID=89533
THEN this shows up a few minutes later...
[40267] (05/08 10:11:47.256):{0x1434} {John@xxxxx} Starting calendar rescan
[40373] (05/08 10:11:47.318):{0x1434} {John@xxxxx} Queuing notification of modified appointment. EntryId=90312 (delay processing 2 seconds)
[40373] (05/08 10:11:47.318):{0x1434} {John@xxxxx} Queuing notification of modified appointment. EntryId=90311 (delay processing 2 seconds)
[30019] (05/08 10:11:47.318):{0x1434} {John@xxxxx} MAPIMailbox:

oICS ICS Synch Successful
[40701] (05/08 10:11:47.318):{0x1434} {John@xxxxx} Calendar rescan completed
Does that offer any insight?