I know my experience with other mobile devices has been that you want to minimize the "instances" of the calendar that are running. Going from 1-2-3 instances of the calendar increases sync issues tremendously. So 1 instance would be, say, a desktop instance( if your are using that), another would be the 2nd mobile device, and another would be the 3rd mobile device. In addiition if you are using something like Outlook, it maintains a cached copy of all your stuff which is yet another instance. For consistency, if you have to have an absolutely accurate calendar, I would create and delete and accept appointments from one device and one device only. I think where you are now, you want to get one of the calendar instances absolutely correct and then use that as a master and connect the other devices in a de facto read and view only mode. I know it should work like you have it setup and probably would work as setup in a perfect world....but I know from experience your best bet is to keep calendar sync as simple as possible.
