Calendar meetings are intermittently disappearing from a manager's calendar after having been accepted by his administrative assistant with delegate permissions. Most of the meetings that have disappeared have come from a particular meeting organizer. Here's a description of the procedure used by the delegate:
Outlook is configured to open her manager's mailbox every time she opens the app. (We are in an Exchange 2000 Server environment) The Admin Asst. is set to automatically receive notices of the manager's meetings. When she sees that a notice has been received she opens the manager's Inbox, clicks on the calendar review button to confirm the manager's availablity, and then accepts/rejects the meeting as appropriate. Then she goes back into her own Inbox and opens the message to ensure that is says, "Accepted by blah" on "blah" date. If the notice is a cancellation, she will open the notice and click on the "Remove from Calendar" button. Then she moves that meeting notice from the Inbox to her personal folder.

According to the Admin, this worked consistently in Outlook 2000, but now, with Outlook 2002 meetings intermittenly disappear from the manager's calendar.