Out of Office OOF Issue - doesn't work in OWA

I have seen numerous threads, forums, and KB articles discussing various Out of Office issues, but this is one I can't seem to get fixed or find a solution to.  I also have a parallel ticket open with Microsoft Support who are also perplexed and taking their time in getting back to us.

We are in the process of migrating from Exchange 2003 to Exchange 2007 - all in the same org / forest / domain.  Most users are still on Exchange 2003 - and this issue does not plague them.  It does effect everyone on the Exchange 2007 system, however.

We have an Exchange 2007 SP1 farm with a CCR Mailbox Cluster, two Hub Transport servers, and two CAS servers (for OWA only - no RPC over HTTP / Outlook Anywhere or other connections/clients being used here).  When using the Outlook client, Out of Office works fine.  But when using OWA, it 'appears' to work but never actually sends the Out of Office message back to a sender.  It should also be noted that whatever OOF status was set in Outlook does not appear in OWA, and vice versa - they seem to be disconnected and separate - and again, the only method of using OOF that works is via Outlook client.  

I have spent time on the phone w/ MSFT Support verifying Remote Domain is configured correctly at Org > Hub Transport in EMC.  He also had me check the permissions/security on the EWS virtual directory in IIS on the CAS servers, which apparently checked out fine.  MSFT verified the certificate used (third party UC/SAN cert from EnTrust) was good, no issues there.  

Also want to point out that all other functionality in OWA seems to be working fine...

This issue is definitely holding up migrating the remaining 2000+ mailboxes onto Exchange 2007... looking for any assistance or suggestions.

Thanks....
Trevor