I have a web page x.php (in a password protected area of my web site) which has a form and a button which uses the POST method to send the form data and opens x.php#abc. This works pretty well.

However, if the users decides to navigate back in Internet Explorer 7, all the fields in the original x.php get cleared and everything must be typed in again. I cannot save the posted information in a session and I am trying to understand how I can get IE7 to behave the way I want.

I've searched the web and found answers which suggest that the HTTP header should contain explicit caching information. Currently, I've tried this :

session_name("FOO");
session_start();
header("Pragma: public");
header("Expires: Fri, 7 Nov 2008 23:00:00 GMT");
header("Cache-Control: public, max-age=3600, must-revalidate");
header("Last-Modified: Thu, 30 Oct 2008 17:00:00 GMT");

and variations thereof. Without success. Looking at the returned headers with a tool such as WireShark shows me that Apache is indeed honouring my headers.

So my question is: what am I doing wrong?