Exchange plugin query

A customer of mine is using CRM v7.1fS. They have Outlook 2007. They have Exchange integration enabled.

I didn't realise this but when filing an email using the Exchange lite plugin, the email is marked as being filed by the Categories field in Outlook. Does it still change the icon? This customer has reported that since mid December a user is filing emails but they are not showing as filed in the categories field. I have asked them to uninstall the plugin and reinstall it but it still happens.

It says in the user guide on page 113 "Filed e-mails are marked with the message Filed to Sage CRM."

Why would this happen? Any ideas what to suggest?