Is there a way to clear the calendar invitations from the iPhone invite inbox when the Meeting is accepted by a delegate?

I am running an Exchange / Outlook 2010 environment with many mobile users accessing email and calendars with iPhones. Senior Executives have delegated their Calendars to Executive Assistants, who manage them mostly from Outlook. When Meeting requests arrive for the executives, their assistants Accept, Decline or mark as Tentative as the calendar allows.

The executives have only their mail account on their iPhone. The assistants have both their account and the executive's Exchange ActiveSync account on their phones. When the request is handled and a Send Response Now is submitted, the calendar invitation does not get cleared from the Senior Executive's Calendar invitation inbox, or the Calendar invitation inbox on their assistant's phone (which is to say, the Senior Executive's Calendar, which is a secondary calendar at this point) but it does show up properly on their Calendar. It seems the cache doesn't know that the request has been handled and does not clear the flag.

Other than turning off the Calendar, deleting the ActiveSync data and downloading fresh data, is there a way to correct this? I have tried multiple switches and settings, notifications, etc. I have even dabbled in Outlook's Rules, since this is where the delegation occurs. Once a Meeting is accepted, how can it be cleared in the inbox? This is not a badge, as I've turned off badges.

It affects not only the iPhone 4 and 5, but also iPads and iPad Minis running iOS 6.0.1 or better.