Duplicate Meetings on Bosses calander

We have a Boss and his secretary. We are using exchange 2003.
Boss is using Outlook 2003 and Secretary is using Outlook 2007 (just
recently upgraded)
Secretary is Delegate (Editor) of Bosses calendar and they have it setup so
both receive the meeting request email. That way if one is out the other can
accept/deny.
Since secretary upgraded to 2007 anytime someone, other than those two,
sends a meeting request to Boss, it arrives in both their inboxes as wanted.
But now if they both accept the invitation the meeting will show up twice in
the Boss's calendar. When they were both using Outlook 2003 and both
accepted a meeting invite, it would only show up once on the Boss's calendar.

Any ideas on what may cause this or any fixes?