Issue with groups and forwarding

We have an inside salesperson who has a group called abc and that group is in her personal n&a book. When she enters the group name and sends the email all works fine and the 3 internet email address’ are put in place of abc. If she also cc’s that email to someone in our company it works OK and that person sees the 3 names.

Now if the person that was cc’d then forwards that email to someone else in the company the 3 names revert back to the group name of abc.

The abc group is not in our company wide n&a. Why would Domino put the group name back in - in place of the 3 people in the group?

TIA

Frank