WRONG TITLE, using BIS NOT BES

Hello,
I ma having a strange problem with my Blackberry users. Quick breakdown:
1. Using UW-IMAP with sendmail for corporate email.
2. Using BIS
3. Using Thunderbird client

I am having trouble syncing the blackberry with IMAP via the BIS server. I have all the accounts setup for eache user on the BIS server with the sync option selected. BUT, whenever I delete a message from the blackberry using "delete on mailbox and handheld", it does not remove it from the users mail file, and is still visible in mail clients. BUT, and here's the kicker, I have the same setup with my 8830 WE and it DOES work, the 2 way sync is working fine. All my other users are on 8703E with 4.2.1.110 software. I have 4.5 on my 8830.

All mail accounts are the same on the sendmail server and I can see the BIS logins to the imap service.

I cannot seem to find out where my account and other user accounts differ. Could it be related to the software on the BB? I have setup a users account on my BB to test and it still failed, so I wouldn't think the device is the issue.

Any suggestions are appreciated.

Paul