Index: includes/session.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/session.inc,v
retrieving revision 1.91
diff -u -p -r1.91 session.inc
--- includes/session.inc	5 Nov 2010 19:05:02 -0000	1.91
+++ includes/session.inc	11 Nov 2010 09:00:26 -0000
@@ -200,6 +200,9 @@ function _drupal_session_write($sid, $va
           }
         }
       }
+      elseif (variable_get('https', FALSE)) {
+        unset($key['ssid']);
+      }
 
       db_merge('sessions')
         ->key($key)
Index: modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.522
diff -u -p -r1.522 system.install
--- modules/system/system.install	5 Nov 2010 19:05:02 -0000	1.522
+++ modules/system/system.install	11 Nov 2010 09:00:26 -0000
@@ -2910,7 +2910,11 @@ function system_update_7065() {
     'length' => 128,
     'not null' => TRUE,
   );
-  db_change_field('sessions', 'sid', 'sid', $spec);
+  db_drop_primary_key('sessions');
+  db_change_field('sessions', 'sid', 'sid', $spec,
+    array('primary key' => array('sid', 'ssid')));
+  // Delete any sessions with empty session identifier.
+  db_delete('sessions')->condition('sid', '')->execute();
 }
 
 /**