"on duplicate key" question

[Lev Lvovsky]

This is somewhat related to my last question RE conflicting procedure  
argument names, but in regards to multi-row inserts...

suppose the following procedure:
----
DROP PROCEDURE IF EXISTS sp_ImportedUpdate |
CREATE PROCEDURE sp_ImportedUpdate ()
DETERMINISTIC CONTAINS SQL MODIFIES SQL DATA
BEGIN
   INSERT INTO Destination SELECT ID,
                               CONTACT_NAME,
                               CONTACT_EMAIL,
                               CONTACT_PHONE,
                               ADDRESS_1,
                               ADDRESS_2,
                               CITY,
                               PROVINCE,
                               POSTAL_CODE,
                               COUNTRY,
                               CIRCUIT_ID,
                               TIME_ZONE
   FROM ToBeUpdated
   ON DUPLICATE KEY UPDATE
   ID = VALUES(ID),
   CONTACT_NAME = VALUES(CONTACT_NAME),
   CONTACT_EMAIL = VALUES(CONTACT_EMAIL),
   CONTACT_PHONE = VALUES(CONTACT_PHONE),
   ADDRESS_1 = VALUES(ADDRESS_1),
   ADDRESS_2 = VALUES(ADDRESS_2),
   CITY = VALUES(CITY),
   PROVINCE = VALUES(PROVINCE),
   POSTAL_CODE = VALUES(POSTAL_CODE),
   COUNTRY = VALUES(COUNTRY),
   CIRCUIT_ID = VALUES(CIRCUIT_ID),
   TIME_ZONE = VALUES(TIME_ZONE);
END |
-----

Here, 'ToBeUpdated' is a view which highlights changes between to  
tables with the same primary keys, but possibly different values in  
other columns.  The naming scheme here can be tricky, and on first  
glance given previous problems, it would look to fail, because the  
column name in VALUES() is the same as the one on the left.  However,  
this actually works as intended, where the "changed" values are the  
ones being returned by VALUE.  Can someone explain why this is?  I'd  
like to have a solid understanding of the scoping of procedure  
variables which happen to be the same as column names.

thank you!
-lev