Attendee shows up as Required and Optional in Outlook 2007

I have a user that is not part of our domain. His outside email address needs
to be added to an internal distribution list, so I created a contact in AD
for him using his outside email address. I am able to send emails to him and
also if I send an email to the distribution list he is part of he gets the
email. If I set up a meeting in my calendar and invite him, he gets the
invite, but if I make a change to that calendar invite I notice that his name
shows up as a required and optional attendee. What is weird is that only his
name shows up in the Required field and in the Optional field his name shows
up as "Lastname, FirstName " and he never gets the meeting
update. Has anyone seen this type of issue?