Outlook - Forwarded E-Mail from Shared Mailbox gets stuck in Outbox

We are currently running Outlook 2007 and Exchange 2010 - just migrated off Lotus Notes over the last few weeks so still getting to grips with the new environment

I am having an issue with forwarding e-mail from a shared mailbox to another mailbox

For example, I have two mailboxes - USERA and USERB.

In Outlook, USERA has been granted 'Publishing Editor' permissions to USERB mailbox - USERB mailbox has been added under the Account Settings --> Advanced Page and all USERB mailbox/folders are visible under Mail Items when logged in a s USERA

Under the EMC, USERA has been granted permissions to Send on Behalf of USERB (Mail Flow Settings --> Delivery Options)

When logged in as USERA - I can succesfully send on behalf of USERB (New Message - FROM : USERB - to another e-mail account - i.e. USERC) - message goes to USERC - shown as sent on behalf of USERB and the message goes into USERA Sent Items

If, still logged in as USERA, I select an e-mail in USERB mailbox and then click Forward (FROM : USERB - To: USERC) then USERC will successfully recieve the message but the message will remain in USERA Outbox - it does not go into Sent Items

If you go into the Outbox you can successfully delete this message

I have restarted the Exchange server so I know it nothing to do with delayed permissions not filiter through

Is there some additional permission levels that need to be configured