Why doesn't := "Always match?"

[Paul Long]

A man page (http://www.die.net/doc/linux/man/man5/users.5.html) for the 
users file says, "Attribute := Value ... Always matches as a check 
item..." So does that mean, no matter what the value is, it will always 
match the attribute? I don't see that happening. As an experiment, I 
have a supplicant in a WiFi phone with user name of "plong" and password 
of "123". With the following entry in the users file:

    plong    Auth-Type = Local, User-Password := "126"

...I assumed it would match even though the value is different; however, 
it does not match, and the access request is rejected:

  rlm_chap: login attempt by "plong" with CHAP password
  rlm_chap: Using clear text password 126 for user plong authentication.
  rlm_chap: Pasword check failed

To get it to match, I have to have the correct value:

    plong    Auth-Type = Local, User-Password := "123"

which results in this debug output:

  rlm_chap: login attempt by "plong" with CHAP password
  rlm_chap: Using clear text password 123 for user plong authentication.
  rlm_chap: chap user plong authenticated succesfully

In fact, := behaves exactly like == in this case. What's the deal? Why 
doesn't := "always match?" Am I misunderstanding what it means to "match?"

Paul