I raised this issue on the Outlook forum; as the environment is an Exchange 2010 one they said I should raise it here for better answers. So, here it is...
In Outlook 2010, we send email templates created in Word which are completed by the recipient and then sent on from their mailboxes. After KB2687623 was installed, these fail to work correctly. Instead of the recipient seeing the template fields, they simply
get an email with the template information in the body of the email.
We can remove the update, but I'd like to see a permanent fix for this.