FIX: Query parameters were not being cleared when changing filtering.

app/assets/javascripts/discourse/controllers/discovery/topics.js.es6

@@ -19,6 +19,10 @@ const controllerOpts = {
   expandGloballyPinned: false,
   expandAllPinned: false,
 
+  resetParams() {
+    this.setProperties({ order: "default", ascending: false });
+  },
+
   actions: {
 
     changeSort(sortBy) {
@@ -43,8 +47,7 @@ const controllerOpts = {
 
     refresh() {
       const filter = this.get('model.filter');
-
-      this.setProperties({ order: "default", ascending: false });
+      this.resetParams();
 
       // Don't refresh if we're still loading
       if (this.get('discovery.loading')) { return; }

app/assets/javascripts/discourse/lib/url.js.es6

@@ -326,6 +326,11 @@ const DiscourseURL = Ember.Object.extend({
     if (opts.replaceURL) {
       this.replaceState(path);
     } else {
+      const discoveryTopics = this.controllerFor('discovery/topics');
+      if (discoveryTopics) {
+        discoveryTopics.resetParams();
+      }
+
       router.router.updateURL(path);
     }