Support did not mention a specific bug. That's why I didn't mention a bug number in my previous post. A search of bugzilla for "iphone" produces several results. About three of the bugs are related to appointments. I have subscribed to these three:
Bug 36249 – iPhone meeting acceptance Bug 39358 – accept/decline response from iPhone does not update status on attendee's copy of appointment Bug 39429 – Calendar item acceptence from iphone causes local failure notice in outlook