diff --git a/enrol/ajax.php b/enrol/ajax.php
index 8a0bdfc09a7..48b3fca31eb 100644
--- a/enrol/ajax.php
+++ b/enrol/ajax.php
@@ -54,9 +54,9 @@ echo $OUTPUT->header(); // send headers
 
 $manager = new course_enrolment_manager($PAGE, $course);
 
-$outcome = new stdClass;
+$outcome = new stdClass();
 $outcome->success = true;
-$outcome->response = new stdClass;
+$outcome->response = new stdClass();
 $outcome->error = '';
 
 switch ($action) {
@@ -99,6 +99,10 @@ switch ($action) {
             $user->fullname = fullname($user);
             unset($user->id);
         }
+        // Chrome will display users in the order of the array keys, so we need
+        // to ensure that the results ordered array keys. Fortunately, the JavaScript
+        // does not care what the array keys are. It uses user.id where necessary.
+        $outcome->response['users'] = array_values($outcome->response['users']);
         $outcome->success = true;
         break;
     default:
diff --git a/enrol/manual/ajax.php b/enrol/manual/ajax.php
index a9d5bb7f804..b599b95a552 100644
--- a/enrol/manual/ajax.php
+++ b/enrol/manual/ajax.php
@@ -53,9 +53,9 @@ echo $OUTPUT->header(); // send headers
 
 $manager = new course_enrolment_manager($PAGE, $course);
 
-$outcome = new stdClass;
+$outcome = new stdClass();
 $outcome->success = true;
-$outcome->response = new stdClass;
+$outcome->response = new stdClass();
 $outcome->error = '';
 
 switch ($action) {
@@ -79,6 +79,10 @@ switch ($action) {
             }
             $user->extrafields = implode(', ', $fieldvalues);
         }
+        // Chrome will display users in the order of the array keys, so we need
+        // to ensure that the results ordered array keys. Fortunately, the JavaScript
+        // does not care what the array keys are. It uses user.id where necessary.
+        $outcome->response['users'] = array_values($outcome->response['users']);
         $outcome->success = true;
         break;
     case 'enrol':
@@ -135,4 +139,4 @@ switch ($action) {
         throw new enrol_ajax_exception('unknowajaxaction');
 }
 
-echo json_encode($outcome);
\ No newline at end of file
+echo json_encode($outcome);
diff --git a/user/selector/module.js b/user/selector/module.js
index de2f500d804..120fb7865ef 100644
--- a/user/selector/module.js
+++ b/user/selector/module.js
@@ -221,8 +221,9 @@ M.core_user.init_user_selector = function (Y, name, hash, extrafields, lastsearc
 
             // Output each optgroup.
             var count = 0;
-            for (var groupname in data.results) {
-                this.output_group(groupname, data.results[groupname], selectedusers, true);
+            for (var key in data.results) {
+                var groupdata = data.results[key];
+                this.output_group(groupdata.name, groupdata.users, selectedusers, true);
                 count++;
             }
             if (!count) {
@@ -248,13 +249,14 @@ M.core_user.init_user_selector = function (Y, name, hash, extrafields, lastsearc
         output_group : function(groupname, users, selectedusers, processsingle) {
             var optgroup = Y.Node.create('<optgroup></optgroup>');
             var count = 0;
-            for (var userid in users) {
-                var user = users[userid];
-                var option = Y.Node.create('<option value="'+userid+'">'+user.name+'</option>');
+            for (var key in users) {
+                var user = users[key];
+                var option = Y.Node.create('<option value="'+user.id+'">'+user.name+'</option>');
                 if (user.disabled) {
                     option.set('disabled', true);
-                } else if (selectedusers===true || selectedusers[userid]) {
+                } else if (selectedusers===true || selectedusers[user.id]) {
                     option.set('selected', true);
+                    delete selectedusers[user.id];
                 } else {
                     option.set('selected', false);
                 }
diff --git a/user/selector/search.php b/user/selector/search.php
index fcaf74ec3bb..ab282749a76 100644
--- a/user/selector/search.php
+++ b/user/selector/search.php
@@ -78,17 +78,20 @@ if (isset($options['file'])) {
 $userselector = new $classname($name, $options);
 
 // Do the search and output the results.
-$users = $userselector->find_users($search);
-foreach ($users as &$group) {
-    foreach ($group as $user) {
+$results = $userselector->find_users($search);
+$json = array();
+foreach ($results as $groupname => $users) {
+    $groupdata = array('name' => $groupname, 'users' => array());
+    foreach ($users as $user) {
         $output = new stdClass;
         $output->id = $user->id;
         $output->name = $userselector->output_user($user);
         if (!empty($user->disabled)) {
             $output->disabled = true;
         }
-        $group[$user->id] = $output;
+        $groupdata['users'][] = $output;
     }
+    $json[] = $groupdata;
 }
 
-echo json_encode(array('results' => $users));
+echo json_encode(array('results' => $json));