This works in 4.3.1 and prior but does not work in 4.3.2RC's and current CVS.

<?
$myArray[] = 'msgid'."\n";
$myArray[] = '1049987091'."\n";
$myArray[] = '1050930128'."\n";

$fp = fopen("problemFile.php",'w') or die("Unable to open file");
for ($i=0;$i<count($myArray);$i++) {
	if ($i==0) $prefx = "<? Header(\"HTTP/1.0 403 Forbidden\");exit; ?>\n";
	else $prefx = "";
	fwrite($fp,$prefx.$myArray[$i]);
}
	fclose($fp);
?>

The file looks like this, which is correct:
<? Header("HTTP/1.0 403 Forbidden");exit; ?>
msgid
1049987091
1050930128

However, under 4.3.2 the file looks like this:
<? Header("HTTP/1.0 403 Forbidden");exit; ?>
msgid1049987091
1050930128

If you modify the code to this, moving the header code to the array, it works under 4.3.2:
<?
$myArray[] = "<? Header(\"HTTP/1.0 403 Forbidden\");exit; ?>\n";
$myArray[] = 'msgid'."\n";
$myArray[] = '1049987091'."\n";
$myArray[] = '1050930128'."\n";

$fp = fopen("problemFile.php",'w') or die("Unable to open file");
for ($i=0;$i<count($myArray);$i++) {
	fwrite($fp,$myArray[$i]);
	echo nl2br($myArray[$i]);
}
	fclose($fp);
?>

The file is correct.