I worked on an interesting issue the other day which rung bells.. many bells. The issue relates to what happens when you have the Outlook setting :
In folders other than the inbox, save replied with original message
Here is where it lives in Outlook 2003 and Outlook 2010
^^ Second check box down from the top
^^ 4th checkbox up from the bottom.
Some time ago we had issues with this, in that with the Enterprise Vault Outlook Addin installed, the reply would instead go to the “normal” place, ie “Sent Items”.
It seems that has been rebroken by the work done for the Outlook 2010 support in EV 9.0.1. A new technote has been raised to cover this whilst the issue is investigated further :