Index: theme/flag.js
===================================================================
--- theme/flag.js	(revision 2106)
+++ theme/flag.js	(working copy)
@@ -129,12 +129,14 @@
   if (userFlags) {
     userFlags = userFlags.split('+');
     for (var n in userFlags) {
-      var flagInfo = userFlags[n].match(/(\w+)_(\d+)/);
-      var flagName = flagInfo[1];
-      var contentId = flagInfo[2];
-      // User flags always default to off and the JavaScript toggles them on.
-      if (templates[flagName + '_' + contentId]) {
-        $('.flag-' + flagName.flagNameToCSS() + '-' + contentId, context).after(templates[flagName + '_' + contentId]).remove();
+      if (userFlags.hasOwnProperty(n)) {
+        var flagInfo = userFlags[n].match(/(\w+)_(\d+)/);
+        var flagName = flagInfo[1];
+        var contentId = flagInfo[2];
+        // User flags always default to off and the JavaScript toggles them on.
+        if (templates[flagName + '_' + contentId]) {
+          $('.flag-' + flagName.flagNameToCSS() + '-' + contentId, context).after(templates[flagName + '_' + contentId]).remove();
+        }
       }
     }
   }