Index: vud.module
===================================================================
--- vud.module	(revision 438)
+++ vud.module	(working copy)
@@ -9,6 +9,18 @@
 module_load_include('inc', 'vud', 'vud.theme');  // Include the theme.inc file.
 
 /**
+ * Implementation of hook_init().
+ */
+function vud_init() {
+  // Expire anonymous sessions early for Pressflow (30 minutes)
+  // See issue #672566
+  $now = time();
+  if (!empty($_SESSION['vud_timestamp']) && $now - $_SESSION['vud_timestamp'] > 60 * 30) {
+    unset($_SESSION['vud_timestamp']);
+  }
+}
+
+/**
  * Implementation of hook_help().
  */
 function vud_help($path, $arg) {
Index: vud.theme.inc
===================================================================
--- vud.theme.inc	(revision 438)
+++ vud.theme.inc	(working copy)
@@ -165,6 +165,12 @@
     $variables['class_down'] = 'down-inactive';
   }
 
+  // Set timestamp in session to force anonymous sessions in Pressflow
+  // See issue #672566
+  if ($user->uid === 0 && empty($_SESSION['vud_timestamp'])) {
+    $_SESSION['vud_timestamp'] = time();
+  }
+	
   $token_up = drupal_get_token("vote/$type/$content_id/1/$tag/$widget_theme");
   $token_down = drupal_get_token("vote/$type/$content_id/-1/$tag/$widget_theme");