Index: lib/filterStorage.js
===================================================================
--- a/lib/filterStorage.js
+++ b/lib/filterStorage.js
@@ -192,21 +192,20 @@
   /**
    * Replaces the list of filters in a subscription by a new list
    * @param {Subscription} subscription filter subscription to be updated
    * @param {Filter[]} filters new filter list
    */
   updateSubscriptionFilters(subscription, filters)
   {
     removeSubscriptionFilters(subscription);
-    subscription.oldFilters = subscription.filters;
+    let oldFilters = subscription.filters;
     subscription.filters = filters;
     addSubscriptionFilters(subscription);
-    filterNotifier.emit("subscription.updated", subscription);
-    delete subscription.oldFilters;
+    filterNotifier.emit("subscription.updated", subscription, oldFilters);
   },
 
   /**
    * Adds a user-defined filter to the list
    * @param {Filter} filter
    * @param {SpecialSubscription} [subscription]
    *   particular group that the filter should be added to
    * @param {number} [position]