--- includes/bootstrap.inc
+++ includes/bootstrap.inc
@@ -499,6 +499,8 @@
  * @see page_set_cache
  */
 function drupal_page_header() {
+  global $user;
+  
   if (variable_get('cache', 0)) {
     if ($cache = page_get_cache()) {
       bootstrap_invoke_all('init');
@@ -517,7 +519,7 @@
       $none_match = !empty($_SERVER['HTTP_IF_NONE_MATCH']) ? $_SERVER['HTTP_IF_NONE_MATCH'] == $etag : NULL;
 
       // The type checking here is very important, be careful when changing entries.
-      if (($modified_since !== NULL || $none_match !== NULL) && $modified_since !== false && $none_match !== false) {
+      if (!$user->uid && ($modified_since !== NULL || $none_match !== NULL) && $modified_since !== false && $none_match !== false) {
         header('HTTP/1.0 304 Not Modified');
         exit();
       }
@@ -525,6 +527,7 @@
       // Send appropriate response:
       header("Last-Modified: $date");
       header("ETag: $etag");
+      header("Cache-Control: must-revalidate");
 
       // Determine if the browser accepts gzipped data.
       if (@strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') === false && function_exists('gzencode')) {