I tried:

- typing the address in its entirety (as mentioned in item 1).
- clicking on To: and selecting the address from Contacts.

In both cases, Outlook pulled email address from the recipient's entry in
the GAL, not the Contacts list.  This was confirmed by double-clicking on his
display name, and getting the GAL-entry properties box.

In addition, I tried changing the spelling of the first name in my Contacts,
but it still picks off the GAL.

In the recipient's properties in the GAL (in the E-mail addresses tab), it
lists his email addresses (each preceded by "smtp:"); the list includes the
address in my Contacts (which it lists third).  I suspect it is switching to
the GAL entry because it looks there and finds the address.  But for some
reason the message is not sent to the Contacts entry.  

I would have preferred Outlook keep things simple and only send to the
address I specify.  I welcome any insights that might help me solve this
problem.  Presently, there is no way to send emails to the recipient from my
PC.