new contacts not visible

The scenario: Microsoft Exchange 5.5 on an NT4 server,
with clients running Outlook 2000 on Windows 2000
workstations.

One user, the manager, has his Outlook contacts
accessible by his assistant. That is, on the
assistant's Outlook, she can access the manager's
Inbox, Deleted Items, Sent Items, etc.

Normally, the assistant can make a new entry from her
computer into the manager's Contacts. But recently,
new entries are not appearing on the manager's computer,
even though they show up in the manager's Contacts as
displayed on the assistant's computer.

I made sure the assistant has Owner-level permission to
the manager's Contacts. Any other suggestions?