Index: mollom.module
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/mollom/mollom.module,v
retrieving revision 1.2.2.181
diff -u -p -r1.2.2.181 mollom.module
--- mollom.module	1 Nov 2010 16:41:06 -0000	1.2.2.181
+++ mollom.module	4 Nov 2010 19:56:34 -0000
@@ -1696,6 +1696,11 @@ function mollom_pre_render_mollom($eleme
 
     // Prevent the page cache from storing a form containing a CAPTCHA element.
     $GLOBALS['conf']['cache'] = CACHE_DISABLED;
+    // Pressflow in CACHE_EXTERNAL caching mode additionally requires to mark
+    // this request as non-cacheable to bypass external caches (e.g., Varnish).
+    if (function_exists('drupal_page_is_cacheable')) {
+      drupal_page_is_cacheable(FALSE);
+    }
 
     $data = array();
     if (!empty($form_state['mollom']['response']['session_id'])) {