Not sure it's necessarily an OS issue. "what we have here, is a failure to communicate" there is a communication issue with which appointments go to which BB (CICAL) calendar and Outlook can't keep up and creates doubles, triples etc. I have had this issue in the past BUT I am on a BIS. I tell you this 'cause since you are BES you may need all of your CICAL books for creating or accepting invites. Someone please jump in to correct me.
What I have done is a wipe > resend service books> remove all but one CICAL service book > make all the necessary corrections in Outlook calendar (deleting all doubles and triplicate entries) > make a temporary change to DM -computer calendar overwrites device> sync Outlook. - Don't forget to configure DM back to the original calendar settings when you are done. I "THINK" you can now resend the service books and future made calendar invites will be on the corrrect calendars.