Outlook 2003, SBS 2003, Exchange - search fails - advanced search does not on public folder

We have Exchange on small business server 2003.  Several weeks ago Outlook (2003, 2007 running on both XP and 7) began to fail in finding individuals in a shared public address list.  Entering a last name value into the fast search bar found nothing.  However, if the last name was put in the last name field of advanced search the individual was located.  Any thoughts on what could be causing this behavior?

Any insight would be appreciated.

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RCFoulk