After running Apache2 with PHP 4.2.3 as a CGI binary (in a stable configuration) for quite some time, I decided to switch to PHP 4.3.0 and try running PHP as an Apache2 module.  Just to be sure that everything would run smoothly, I installed Apache 2.0.43 to a fresh directory, and configured PHP 4.3.0 to use the php4apache2.dll as per the instructions.  No extenstions were configured to load in the php.ini file.  After testing, I realized that browsers were not reloading the page.  Over 20 clients running different versions of Internet Explorer reported this, and said that changing the "Check for newer versions of stored pages" option did not alleviate the problem.  I tried a PHP script that, when added to a page, would force the content to not be cached to no avail.  The script was:

<?php
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");    // Date in the past
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); 
                                                     // always modified
header("Cache-Control: no-store, no-cache, must-revalidate");  // HTTP/1.1
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");                          // HTTP/1.0
?>


I also tried the PHP script

<?php
session_cache_limiter('nocache');
?>

to no avail.  I checked php.ini and found that nocache was already specified by this line:

session.cache_limiter = nocache

I also tried altering this line:

session.cache_expire = 180

to 0 minutes, but that did not solve the problem.  However, I did try running PHP as a CGI binary, and that eliminated the problem altogether.  I conclude that there is something in running PHP as an Apache2 module that is causing this problem.