Appointment not showing in calendar

Since I am the delegate for my managers Outlook, I
scheduled a meeting for my manager to meet with two other
people, it appeared in my managers calendar and the two
other persons calendars, but when I had to reschedule the
meeting to a different time, the change was made and it
was reflected in the two other persons calendar, but not
in my managers. In turn he missed his meeting (not that
it is important here) This has happened a few times.

Has this happened to anyone else? Does anyone have any
suggestions to help me.

Thanks much,

Nicholas