Still the annoying "followup creates new ticket"

Hi,
I already posted something about follow ups not attaching to corresponding tickets, but we're now in the beginning of using them on a regular basis, so I just need to make it work before deployment.
The problem:
For a given ticket, we sometimes use the "forward" functionality to forward the ticket to external contract companies.
After solving the ticket, usually they reply to the original forwarded message.
This new email ALWAYS creates a new ticket.
One example:
Ticket 102456, subject: Drive disquetes avariada!
Forwarded email:
-----Original Message-----
From: Helpdesk [mailto:helpdesk@xxxxx]
Sent: terça-feira, 29 de Junho de 2004 10:05
To: helpdesk@yyyyyy
Subject: [TicketNr#: 102456-FW] Drive disquetes avariada!
Reply:
From: "HELPDESK"
participants (1)
-
Duarte Cordeiro