diff --git a/CRM/Core/Config/MagicMerge.php b/CRM/Core/Config/MagicMerge.php
index ffb7e6434708..801f803f3b4e 100644
--- a/CRM/Core/Config/MagicMerge.php
+++ b/CRM/Core/Config/MagicMerge.php
@@ -318,10 +318,6 @@ public function __set($k, $v) {
     unset($this->cache[$k]);
     $type = $this->map[$k][0];
 
-    // If foreign name is set, use that name (except with callback types because
-    // their second parameter is the object, not the foreign name).
-    $name = isset($this->map[$k][1]) && $type != 'callback' ? $this->map[$k][1] : $k;
-
     switch ($type) {
       case 'setting':
       case 'setting-path':
@@ -331,12 +327,12 @@ public function __set($k, $v) {
       case 'callback':
       case 'boot-svc':
         // In the past, changes to $config were not persisted automatically.
-        $this->cache[$name] = $v;
+        $this->cache[$k] = $v;
         return;
 
       case 'local':
         $this->initLocals();
-        $this->locals[$name] = $v;
+        $this->locals[$k] = $v;
         return;
 
       default:
diff --git a/tests/phpunit/CRM/Core/Config/MagicMergeTest.php b/tests/phpunit/CRM/Core/Config/MagicMergeTest.php
new file mode 100644
index 000000000000..250075df5bae
--- /dev/null
+++ b/tests/phpunit/CRM/Core/Config/MagicMergeTest.php
@@ -0,0 +1,74 @@
+<?php
+/*
+ +--------------------------------------------------------------------+
+ | CiviCRM version 5                                                  |
+ +--------------------------------------------------------------------+
+ | Copyright CiviCRM LLC (c) 2004-2019                                |
+ +--------------------------------------------------------------------+
+ | This file is a part of CiviCRM.                                    |
+ |                                                                    |
+ | CiviCRM is free software; you can copy, modify, and distribute it  |
+ | under the terms of the GNU Affero General Public License           |
+ | Version 3, 19 November 2007 and the CiviCRM Licensing Exception.   |
+ |                                                                    |
+ | CiviCRM is distributed in the hope that it will be useful, but     |
+ | WITHOUT ANY WARRANTY; without even the implied warranty of         |
+ | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.               |
+ | See the GNU Affero General Public License for more details.        |
+ |                                                                    |
+ | You should have received a copy of the GNU Affero General Public   |
+ | License and the CiviCRM Licensing Exception along                  |
+ | with this program; if not, contact CiviCRM LLC                     |
+ | at info[AT]civicrm[DOT]org. If you have questions about the        |
+ | GNU Affero General Public License or the licensing of CiviCRM,     |
+ | see the CiviCRM license FAQ at http://civicrm.org/licensing        |
+ +--------------------------------------------------------------------+
+ */
+
+/**
+ *
+ * @package CiviCRM
+ * @copyright CiviCRM LLC (c) 2004-2019
+ * $Id: $
+ *
+ */
+
+/**
+ * Class CRM_Core_Config_MagicMergeTest
+ * @group headless
+ */
+class CRM_Core_Config_MagicMergeTest extends CiviUnitTestCase {
+
+  public function getOverrideExamples() {
+    return [
+      // Check examples of a few different types
+      ['configAndLogDir', '/tmp/zoo'],
+      ['maxAttachments', '112358'],
+      ['initialized', 'for sure'],
+      ['userFrameworkBaseURL', 'http://example.com/use/the/framework/luke'],
+      ['inCiviCRM', 'all the data'],
+      ['cleanURL', 'as clean as a url can be'],
+      ['defaultCurrencySymbol', ':)'],
+    ];
+  }
+
+  /**
+   * @param string $field
+   * @param mixed $tempValue
+   * @dataProvider getOverrideExamples
+   */
+  public function testTempOverride($field, $tempValue) {
+    $config = CRM_Core_Config::singleton();
+    $origValue = $config->{$field};
+
+    $config->{$field} = $tempValue;
+    $this->assertEquals($tempValue, $config->{$field});
+
+    $config = CRM_Core_Config::singleton();
+    $this->assertEquals($tempValue, $config->{$field});
+
+    $config = CRM_Core_Config::singleton(TRUE, TRUE);
+    $this->assertEquals($origValue, $config->{$field});
+  }
+
+}