This bug is security related. The password of any user which is authenticated via Apache is still accessible through $PHP_AUTH_PW to any user who is able to execute php-scripts. I'm using mod_auth_samba to authenticate users with their windows-passwords.
http://www.php.net/manual/en/features.http-auth.php states, that "In order to prevent someone from writing a script which reveals the password for a page that was authenticated through a traditional external mechanism, the PHP_AUTH variables will not be set if external authentication is enabled for that particular page. In this case, the $REMOTE_USER variable can be used to identify the externally-authenticated user.

Configuration Note: PHP uses the presence of an AuthType directive to determine whether external authentication is in effect. Remember to avoid this directive for the context where you want to use PHP authentication (otherwise each authentication attempt will fail)."

Unless I'm completely mistaken, $PHP_AUTH_USER and $PHP_AUTH_PW are set, regardless of the existence of the 'AuthType'-directive.
________________________________________________________
testme.php:
<?=$PHP_AUTH_USER?>
<br>
<?=$PHP_AUTH_PW?>
<br>
<?=$REMOTE_USER?>

Configuration:
---------------
* SuSE Linux 7.3
* Apache 1.3.23:
...
  <Location "/testme.php">
    AuthType Basic
    Options FollowSymLinks
    AllowOverride None
    AuthSambaEnabled On
    AuthAuthoritative On      
    AuthName "php_auth_pw Test"
    AuthSambaDomain tiwag:exchange,hvntsna
    require valid-user
    Order Allow,Deny
    Allow from all
  </Location>
...
Compile options:
LIBS="/lib/security/pam_smb_auth.so -lpam /usr/lib/libdbm.so" \
./configure     --prefix=/usr/local/apache \
                --add-module=src/modules/extra/mod_auth_samba.c \
                --enable-module=access \
                --enable-module=actions \
                --enable-module=alias \
                --enable-module=asis \
                --enable-module=auth \
                --enable-module=auth_digest \
                --enable-module=autoindex \
                --enable-module=cgi \
                --enable-module=dir \
                --enable-module=env \
                --enable-module=expires \
                --enable-module=headers \
                --enable-module=imap \
                --enable-module=include \
                --enable-module=info \
                --enable-module=log_config \
                --enable-module=mime \
                --enable-module=mime_magic \
                --enable-module=negotiation \
                --enable-module=setenvif \
                --enable-module=so \
                --enable-module=speling \
                --enable-module=ssl \
                --enable-module=status \
                --enable-module=userdir \
                --server-uid=httpd \
                --server-gid=httpd \
                --with-perl=/usr/bin/perl 

* PHP 4.1.2
Compile options:
./configure --prefix=/usr/local/php \
            --with-apxs=/usr/local/apache/bin/apxs \
            --enable-magic-quotes \
            --with-bz2 \
            --with-java=/usr/lib/java \
            --with-mcrypt \
            --enable-mailparse \
            --with-mysql=/usr/local/mysql \
            --with-ncurses \
            --with-pdflib=/usr/lib \
            --with-mm=/usr/lib \
            --enable-sockets \
            --enable-trans-sid \
            --enable-memory-limit \
            --enable-shared \
            --enable-static \
            --enable-tsrm-pthreads \
            --with-gnu-ld