Lighttpd

My last issue was deleted by accident, so here goes:

No errors in /var/log/lighttpd/errors.log

A few files called lighttp* and later php* appear in /tmp

ahl:/tmp# while true; do ls -l |grep -v sess && echo .; done
-rw------ 1 lighttpd lighttpd 298177 Jan 11 17:52 lighttpd-upload-Ib7A6u
.
rw------ 1 lighttpd lighttpd 816561 Jan 11 17:52 lighttpd-upload-Ib7A6u
.
rw------ 1 lighttpd lighttpd 173760 Jan 11 17:52 lighttpd-upload-GSfToa
rw------ 1 lighttpd lighttpd 1049689 Jan 11 17:52 lighttpd-upload-Ib7A6u
.
rw------ 1 lighttpd lighttpd 386428 Jan 11 17:52 lighttpd-upload-GSfToa
rw------ 1 lighttpd lighttpd 1049689 Jan 11 17:52 lighttpd-upload-Ib7A6u
rw------ 1 lighttpd lighttpd 716660 Jan 11 17:52 phpqwZAOS

My upload.php, pretty basic, should just save the file. It DOES work when the uploaded file is small, for example 341kB.
---------------

<?php 
     header('Content-type: text/html; charset=utf-8');

     $uploadedfile = $_FILES['userfile']['tmp_name'];
    echo "The file uploaded was $uploadedfile.";

     $storefile = $_POST['fnr'] . ".png";

     $command = "cp -v $uploadedfile $storefile"; // save the uploaded file.
     passthru($command); // save 

?>

It seems lighttpd builds several files of around 1MB and then puts them together to one file, phpqwZAOS is seen above.

But when it's too big a file, that file isn't available and doesn't show up in the $_FILES[] array of PHP. Problem with lighttpd passing the file to php?

lighttpd version: lighttpd-1.4.23-r2

OS: alpine linux 2.6.30.8-grsec

Attached strace of a post of a big file.