Description:
------------
This is the php -v from one of the servers:
PHP 5.2.9 with Suhosin-Patch 0.9.7 (cli) (built: Apr  9 2009 
03:31:34)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2009 Zend Technologies

This is another one (macosx):
PHP 5.2.9 (cli) (built: Apr  2 2009 16:07:08) 
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2009 Zend Technologies
with Xdebug v2.0.4, Copyright (c) 2002-2008, by Derick Rethans

Right after my system() call, headers were send. This works 
differently in 5.2.6 and 5.2.8. I've scanned through 
UPDATING/CHANGELOG but couldn't find anything.

I've disabled APC to make sure it's not connected.

php -m:
[PHP Modules]
ctype
date
dom
filter
iconv
libxml
mbstring
mcrypt
mysqli
pcre
Reflection
session
SimpleXML
sockets
SPL
standard
tidy
xml
zlib


Also reproduced with RC1 on 5.3:

PHP 5.3.0RC1 (cli) (built: Apr  9 2009 15:45:09) 
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2009 Zend Technologies

Reproduce code:
---------------
<?php
ob_start();
system('file -i -b /path/file.txt');
$contents = ob_get_contents();
ob_end_clean();
var_dump(headers_sent($file, $line), $file, $line);

Expected result:
----------------
headers_sent() should return false.

Actual result:
--------------
headers_sent() returns true, with empty $file and $line = 0.