Sending 304 - Headers are altered by apache?

Hi all I'm writing a pear package which contains some js/css files. Obviously the files aren't available to the webserver's webroot (I'm using apache2). I've created a script that performs a readfile on the file from the data_dir (I'm using a replace task in my package.xml). So far all is well... To increase performance I'm trying to support the Last-Modified and ETag headers. This triggers a browser to use their caching and even (Firefox does this) omit the HTTP call to the file! So I have a test.php which serves an html doc with a link rel="stylesheet" href="test.php?resource=stylesheet". The latter produces a css doc. However... Sending the headers when I'm sending the initial data (status 200) works, I'm getting the correct Last-Modified and ETag. The second time I'm requesting the file something weird happens: I'm not getting all HTTP Headers that I'm expecting. the X-Powered-By is missing as is the Last-Modified. I'm using FirePHP, but all the Wf-... headers are absent. The only headers I'm getting are: HTTP/1.0 304 Not Modified Date Mon, 27 Oct 2008 17:21:13 GMT Server Apache/2.2.9 (Debian) PHP/5.2.6-5 with Suhosin-Patch Connection close Etag "a49362004946ee139eccb3d077738c44" (I used Wireshark to tcpdump and this is indeed what happens) Note that this only happens when I'm looking at test.php, directly looking at test.php?resource=stylesheet gives me normal, expected headers. As far as I can see the only difference between the requests is that the referer is present when using test.php Somehow this was causing my browser to alternate between sending the If-Modified-Since/If-None-Match headers and omitting them (resulting in sending the data every two times it was requested). When I'm testing right now I'm getting the expected result which is a 200, a 304 and my browser doesn't ask for the file anymore (pressing F5 repeatedly). I know that the PHP process is executed, I'm logging to a file and I'm seeing the process for the specific file. Does anyone know what is happening here?