ob_flush and flush does not work in appweb

Question

This code works well in apache. It pushes a message to the client every second.

But it doesn't work in appweb. Instead, it pushes a message to the client when all message are collected

This is the php code:

<?php
set_time_limit(0);
ob_start();
$i = 1;
while ($i<10) {
    echo $i++;
    ob_flush();
    flush();
    sleep(1);
}
?>

I used the default configuration.