SCRIPT
------

function cmpfunc($a,$b)
{
    echo "*$a**$b*<BR>";
    echo strtr("*$a**$b*<BR>","\0","_");
    
    if ($a<$b) return -1;
    else if ($a==$b) return 0;
    else return 1;
}

$a=array("a" => 1, "b" => 2);

uksort($a,cmpfunc);

OUTPUT
------

*a
*a_**b_*
*a
*a_**b_*


CONFIGURE
---------

./configure --with-apxs=/usr/local/bin/apxs \
--with-config-file-path=/usr/local/apache/conf \
--with-pgsql=/usr/local/ --with-gd=$HOME/ \
--with-snmp --with-sysvsem --with-sysvshm

Apache version: 1.3.11
The same thing happens on Linux with PHP 3.0.12.