With output buffering enabled, if the user presses the stop button in their web client on a page which is executing slowly, when the code completes the page results are written to the apache error_log.

Run the included script and hit the stop button before it completes. The page output (numbers) will be written to the error_log.

<?php
ob_start ();
for ($i = 0; $i < 50000; $i++) {
    echo "$i ";
}
?>

Happens on both Linux (RH7) and Solaris (2.7)