Description:
------------
Keeping it simple:

If you have PHP as a Apache's Mod you can send Last-Modified without problems.

If you have PHP as CGI/FastCGI Last-Modified header is not sent as intented, and which is worse, it's sent as: Last-Modified	Thu, 01 Jan 1970 00:00:00 GMT.

The problem with this is that I can't do custom file caching by sending 304 header.

Reproduce code:
---------------
<?php
        header('Last-Modified: mon, 26 oct 2009 18:26:27 GMT');
        header('mtime: mon, 26 oct 2009 18:26:27 GMT');
	print implode('<br />',headers_list());
?>

It will output the same header_list() regardless it's *CGI or as apache mod.

It prints the following:
X-Powered-By: PHP/5.2.10-2ubuntu6
Last-Modified:lun, 26 oct 2009 18:26:27 GMT
mtime: lun, 26 oct 2009 18:26:27 GMT

But received headers are not the same.

Expected result:
----------------
As an Apache Mod:
X-Powered-By	PHP/5.2.10-2ubuntu6
mtime	mon, 26 oct 2009 18:26:27 GMT
Last-Modified	mon, 26 oct 2009 18:26:27 GMT

Actual result:
--------------
As *GCI:
X-Powered-By	PHP/5.2.10-2ubuntu6
mtime	mon, 26 oct 2009 18:26:27 GMT
Last-Modified	Thu, 01 Jan 1970 00:00:00 GMT