Duplicate Outlook calendar entries created after user added to BES

The problem is that when users receive meetings/appointment updates, a new calendar entry is created (instead of updating the original one on the user's mailbox).  If a user is working from .PST, the calendar entry in the personal folder is updated properly while multiple calendar items are created on the server.  I have isolated it in that it only begins when a user is activated on one of our BES, but this is happening to several hundred people.

I created generic user accounts/mailboxes, and sent meetings and updates back and forth (worked fine).  I added one user to a BES, and once the account was activated on a phone the issues immediately began.  The duplicate entries are only in the user's Exchange-side calendar (and created when it hits the user's Inbox), the wireless device updates appropriately.

We have a mid-sized enterprise environment with our users (WinXP mainly, a mix of Outlook 2003 and 2007 at varying service pack levels) connecting to one of about a dozen Exchange 2003 SP2 servers running on Windows 2003 Ent. SP 1.  We also have a few servers running Blackberry Enterprise Server (one at 4.1.2.25, one at 4.1.4.15) also on 2003 ENT SP1.  Every cdo.dll file is the same version (6.5.7654.12) among every one of the servers.

I have already recommended we patch/update all BES to the latest version, as well as a reboot of the Exchange servers, but this is a large corporate environment so it's not a quick process.  Definitely at a loss here, any help or advice is greatly appreciated!