Troubles using ob, checking PHP connection lost - php

Question

First of all, sorry for my probably bad english...
I'm trying to make a script that works only until an event occur or the connection is stopped. I have to work with output buffers (for logging and debugging reasons) but I noticed that after the connection is lost, everything I try to put in the buffer it doesn't appear.
Here I made a scripts to test this behaviour:
<?php
// here I avoid to let the script stops when the connection is lost
// in order to continue with logging, debugging or wathever
ignore_user_abort(true);
// here there is an utility function that flushes the content
// to let us know if the connection is still active
$fnExec = 0; // this is a variable useful for log the script activity
function is_connection_aborted() {
global $fnExec;
$fnExec++;
// now I get the content of all output buffers and store them,
// then I clean and flush the outputs
$obs = 0;
$contents = Array();
while ($level = ob_get_level()) {
$obContent = ob_get_contents();
array_unshift($contents, $obContent);
ob_clean();
ob_end_flush();
$obs++;
}
echo "\r"; // this is needed in order to have at least a character to flush
flush();
$conn = connection_aborted();
// here I start an output buffer to log what's inside the $contents variable
ob_start();
var_dump($contents);
$fh = fopen('test/fn_'.$fnExec.'.txt', 'w');
fwrite($fh, ob_get_clean());
fclose($fh);
// Now I restore the content in all the output buffers
$count = count($contents) - 1;
$index = 0;
do {
ob_start();
echo $contents[$index];
} while (++$index < $obs);
// Finally returns the value of connection_aborted()
return $conn;
}
// I want to start an output buffer here to manage the output of the script
ob_start();
// This is a simple script that run at most for 5 seconds and print an incremental
// number each iteration, after slept 2 seconds.
// It can be stopped aborting the connection!
$start = time();
$attempts = 0;
while (true) {
echo ++$attempts."\r\n";
if (is_connection_aborted() || (time() - $start) > 5) {
break;
}
sleep(2);
}
// Here I get the content of the output buffer
$content = ob_get_clean();
// And finally I log the content in a file
$fh = fopen('test/test_ob.txt', 'w');
fwrite($fh, $content);
fclose($fh);
Now to the test!
I leave the connection opened up to 2 seconds, and so I expect to see only 1-2 iterations and then a final output like '1 2 3' in the 'test/test_ob.txt' file.
The result, instead, is that I have the file 'test/test_ob.txt' empty but also the file log of the fn()'s execution! It seems like every ob_start() after the connection is lost, will be filled with anything!
Why do output buffers work only until the connection is lost? Is the loss of connection really the problem?
Thanks in advance!