FIX: default user preferenced categories are not updating in admin site setting UI.

app/assets/javascripts/admin/components/site-setting.js.es6

@@ -6,37 +6,45 @@ import showModal from "discourse/lib/show-modal";
 import AboutRoute from "discourse/routes/about";
 
 export default Component.extend(BufferedContent, SettingComponent, {
+  updateExistingUsers: null,
+
   _save() {
-    const defaultCategoriesSettings = [
-      "default_categories_watching",
-      "default_categories_tracking",
-      "default_categories_muted",
-      "default_categories_watching_first_post"
-    ];
     const setting = this.buffered;
-    const key = setting.get("setting");
-    const value = setting.get("value");
+    return SiteSetting.update(setting.get("setting"), setting.get("value"), {
+      updateExistingUsers: this.updateExistingUsers
+    });
+  },
 
-    if (defaultCategoriesSettings.includes(key)) {
-      AboutRoute.create()
-        .model()
-        .then(result => {
-          const controller = showModal("site-setting-default-categories", {
-            model: {
-              count: result.stats.user_count,
-              key: key.replace(/_/g, " ")
-            },
-            admin: true
-          });
+  actions: {
+    update() {
+      const defaultCategoriesSettings = [
+        "default_categories_watching",
+        "default_categories_tracking",
+        "default_categories_muted",
+        "default_categories_watching_first_post"
+      ];
+      const key = this.buffered.get("setting");
 
-          controller.set("onClose", () => {
-            return SiteSetting.update(key, value, {
-              updateExistingUsers: controller.updateExistingUsers
+      if (defaultCategoriesSettings.includes(key)) {
+        AboutRoute.create()
+          .model()
+          .then(result => {
+            const controller = showModal("site-setting-default-categories", {
+              model: {
+                count: result.stats.user_count,
+                key: key.replace(/_/g, " ")
+              },
+              admin: true
+            });
+
+            controller.set("onClose", () => {
+              this.updateExistingUsers = controller.updateExistingUsers;
+              this.send("save");
             });
           });
-        });
-    } else {
-      return SiteSetting.update(key, value);
+      } else {
+        this.send("save");
+      }
     }
   }
 });

app/assets/javascripts/admin/templates/components/site-setting.hbs

@@ -6,7 +6,7 @@
 </div>
 {{#if dirty}}
   <div class='setting-controls'>
-    {{d-button class="ok" action=(action "save") icon="check"}}
+    {{d-button class="ok" action=(action "update") icon="check"}}
     {{d-button class="cancel" action=(action "cancel") icon="times"}}
   </div>
 {{else if setting.overridden}}