General - Warning about headers when "register_shutdown_function" used

When "register_shutdown_function" is used in the code, the following warning is issued:
--
Warning: Cannot modify header information - headers already sent in Unknown on line 0
--
All goes well when xdebug.so is not used.
This bug causes PEAR packages to have problems

PHP Code:

PHP version is 5.0.0 stable, not -dev (can't choose such an option)

Sample code:

<?php

function logit($x)
{
$f = fopen("/tmp/logit.txt", "a");
fwrite($f, "$x\n");
fclose($f);
}

function sayonara()
{
}

register_shutdown_function("sayonara");

?>