[squid-users] Authentication problem

HI List

I have squid-3.2.3 configured to make use of negotiate, and to
authenticate certain users. However the following config doesn't work

acl userA proxy_auth warren
acl userB proxy_auth testb

http_access allow userA
http_access allow userB
http_access deny all

userA successfully authenticates and can browse. userB however
obviously doesn't match userA acl and just gets presented with the
cache denied page.
Debugging the acl shows that it never moves passed the userA acl and
doesn't continue onto authenticating the 'testb' user.

What am I doing wrong here?

thx

-- 
.warren