PHP preg_replace_callback with unicode

I wrote a simple script below to simulate my problem. Both my string and pattern contain unicode characters. Basically, if I run it from command line (php -f test.php), it prints "match" as expected. But if I run it through web server (apache, http://localhost/test.php), it prints "no match". I am using PHP 5.3. I am sure both use the same php.ini. Any idea why it behaves differently? How do I make it work through web server? Thanks ----- <?php function myCallback($matches) { return $matches[0]; //do nothing, test only } $value = 'aaa äää'; $pattern = '/(\bäää)/u'; $value = preg_replace_callback($pattern, 'myCallback', $value, -1, $count); if ($count > 0) { echo "match"; } else { echo 'no match'; } ?>