header gives different results with post

When I submit a post to the following page rather than a get the download screen in IE 5.5SP2 appears twice. Is there any way around this? I definitely need to use post since the length of the string being sent is fairly long. <?php header("Content-type: application/octet-stream"); header('Content-Disposition: attachment;filename="results.csv"');// Try to name the output file 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 /*$nocache = 'Cache-Control: no-cache'; */ // HTTP/1.1 //header($nocache); header('Content-Transfer-Encoding: binary'); // Binary data echo "test"; ?> Thanks.