Yes sir,
When I select the Members Tab in my team profile, the new guest is indicated as --new-- as well as in the Personnel Tab versus the correct name.
In the Sandbox profile I entered John Doe as the New Guest Member and it works as designed just as my Agency login does. We seem to have narrowed it down to the team profile configuration. An additional piece of information is that this not 'working as designed' issue is with every team member login, not just mine, except for the MM system administrator.
Sorry I have given you a tough one.
Pete