diff --git a/app/assets/javascripts/admin/routes/admin-user-index.js.es6 b/app/assets/javascripts/admin/routes/admin-user-index.js.es6
index e2951ff2d80..6767e098b2e 100644
--- a/app/assets/javascripts/admin/routes/admin-user-index.js.es6
+++ b/app/assets/javascripts/admin/routes/admin-user-index.js.es6
@@ -19,6 +19,7 @@ export default Discourse.Route.extend({
     controller.setProperties({
       originalPrimaryGroupId: model.get("primary_group_id"),
       availableGroups: this._availableGroups,
+      customGroupIdsBuffer: null,
       model
     });
   }
diff --git a/test/javascripts/acceptance/admin-user-index-test.js.es6 b/test/javascripts/acceptance/admin-user-index-test.js.es6
index 0e8ee0c6616..36e773f0a30 100644
--- a/test/javascripts/acceptance/admin-user-index-test.js.es6
+++ b/test/javascripts/acceptance/admin-user-index-test.js.es6
@@ -1,6 +1,37 @@
 import { acceptance } from "helpers/qunit-helpers";
 
-acceptance("Admin - User Index", { loggedIn: true });
+acceptance("Admin - User Index", {
+  loggedIn: true,
+  pretend(server, helper) {
+    server.get("/groups/search.json", () => {
+      return helper.response([
+        {
+          id: 42,
+          automatic: false,
+          name: "Macdonald",
+          user_count: 0,
+          alias_level: 99,
+          visible: true,
+          automatic_membership_email_domains: "",
+          automatic_membership_retroactive: false,
+          primary_group: false,
+          title: null,
+          grant_trust_level: null,
+          has_messages: false,
+          flair_url: null,
+          flair_bg_color: null,
+          flair_color: null,
+          bio_raw: null,
+          bio_cooked: null,
+          public_admission: false,
+          allow_membership_requests: true,
+          membership_request_template: "Please add me",
+          full_name: null
+        }
+      ]);
+    });
+  }
+});
 
 QUnit.test("can edit username", async assert => {
   /* global server */
@@ -41,3 +72,41 @@ QUnit.test("can edit username", async assert => {
     "new-sam"
   );
 });
+
+QUnit.test("will clear unsaved groups when switching user", async assert => {
+  await visit("/admin/users/2/sam");
+
+  assert.equal(
+    find(".display-row.username .value")
+      .text()
+      .trim(),
+    "sam",
+    "the name should be correct"
+  );
+
+  await fillIn(".admin-group-selector .filter-input", "Macdonald");
+  await click(".admin-group-selector .filter-input");
+  await keyEvent(".admin-group-selector .filter-input", "keydown", 13);
+
+  assert.equal(
+    find('.admin-group-selector span[title="Macdonald"]').length,
+    1,
+    "group should be set"
+  );
+
+  await visit("/admin/users/1/eviltrout");
+
+  assert.equal(
+    find(".display-row.username .value")
+      .text()
+      .trim(),
+    "eviltrout",
+    "the name should be correct"
+  );
+
+  assert.equal(
+    find('.admin-group-selector span[title="Macdonald"]').length,
+    0,
+    "group should not be set"
+  );
+});
diff --git a/test/javascripts/helpers/create-pretender.js.es6 b/test/javascripts/helpers/create-pretender.js.es6
index 08f530d839a..ab9b6a6b7dd 100644
--- a/test/javascripts/helpers/create-pretender.js.es6
+++ b/test/javascripts/helpers/create-pretender.js.es6
@@ -528,6 +528,14 @@ export default function() {
       });
     });
 
+    this.get("/admin/users/1.json", () => {
+      return response(200, {
+        id: 1,
+        username: "eviltrout",
+        admin: true
+      });
+    });
+
     this.get("/admin/users/2.json", () => {
       return response(200, {
         id: 2,