PHP IE7 and SSL caching issue

I ran into a problem yesterday regarding a flash application running over an SSL connection using IE7. The flash application in question is passed a php script via the url which returns xml as the output; something like this: main.swf?script_file=script.php. I don't know all the complete details, but apparently over an SSL connection IE attempts to cache the xml which is passed to the swf. PHP by default does not cache php scripts. So since in this case the xml is created via a php script, IE cannot cache the xml and instead it returns an error (why??). So the swf itself loads, but will not get passed the xml file, which causes the application to not work properly. There's a lot of confusing/contradictory information regarding this out on the web, but it seems to be a bug in IE. Regardless of the exact cause, the fix is to explicitly tell your php script (the script.php file in the example above) to cache the output by setting these headers:

header('Cache-Control: cache, must-revalidate');
header('Pragma: public');