diff -u b/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
--- b/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2624,8 +2624,8 @@
     // Allow modules to react on language system initialization in multilingual
     // environments.
     bootstrap_invoke_all('language_init');
-    // @TODO remove after http://drupal.org/node/1859110 is resolved.
-    drupal_container()->get('config.factory')->resetConfig();
+    // @todo D8: Remove after http://drupal.org/node/1859110.
+    drupal_container()->get('config.factory')->reset();
   }
 }
 
diff -u b/core/includes/config.inc b/core/includes/config.inc
--- b/core/includes/config.inc
+++ b/core/includes/config.inc
@@ -189,7 +189,7 @@
         $data = $source_storage->read($name);
         $target_storage->write($name, $data);
       }
-      $factory->resetConfig($name);
+      $factory->reset($name);
     }
   }
 }
diff -u b/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
--- b/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -194,15 +194,18 @@
    *   The configuration object.
    */
   public function setData(array $data) {
+    $this->replaceData($data);
     // A load would destroy the data just set (for example on import).
     $this->isLoaded = TRUE;
-    return $this->setDataReal($data);
+    return $this;
   }
 
   /**
    * Replaces the data of this configuration object.
    *
-   * This function is separate from setData to avoid load() state tracking.
+   * This function is separate from setData() to avoid load() state tracking.
+   * A load() would destroy the replaced data (for example on import). Do not
+   * call set() when inside load().
    *
    * @param array $data
    *   The new configuration data.
@@ -210,9 +213,7 @@
    * @return Drupal\Core\Config\Config
    *   The configuration object.
    */
-  protected function setDataReal(array $data) {
-    // A load would destroy the data just set (for example on import). Do not
-    // set when inside load().
+  protected function replaceData(array $data) {
     $this->data = $data;
     $this->resetOverriddenData();
     return $this;
@@ -371,11 +372,11 @@
     $data = $this->storage->read($this->name);
     if ($data === FALSE) {
       $this->isNew = TRUE;
-      $this->setDataReal(array());
+      $this->replaceData(array());
     }
     else {
       $this->isNew = FALSE;
-      $this->setDataReal($data);
+      $this->replaceData($data);
     }
     $this->notify('load');
     $this->isLoaded = TRUE;
@@ -461,8 +462,7 @@
       $this->load();
     }
     // Preserve integer keys so that config keys are not changed.
-    $this->data = NestedArray::mergeDeepArray(array($this->data, $data_to_merge), TRUE);
-    $this->resetOverriddenData();
+    $this->replaceData(NestedArray::mergeDeepArray(array($this->data, $data_to_merge), TRUE));
     return $this;
   }
 }
diff -u b/core/lib/Drupal/Core/Config/ConfigFactory.php b/core/lib/Drupal/Core/Config/ConfigFactory.php
--- b/core/lib/Drupal/Core/Config/ConfigFactory.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactory.php
@@ -38,7 +38,12 @@
    */
   protected $eventDispatcher;
 
-  protected $configs = array();
+  /**
+   * Cached configuration objects.
+   *
+   * @var array
+   */
+  protected $cache = array();
 
   /**
    * Constructs the Config factory.
@@ -66,50 +71,53 @@
   public function get($name) {
     global $conf;
 
-    if (isset($this->configs[$name])) {
-      return $this->configs[$name];
+    if (isset($this->cache[$name])) {
+      return $this->cache[$name];
     }
 
-    $this->configs[$name] = new Config($name, $this->storage, $this->eventDispatcher);
-    return $this->configs[$name]->init();
+    $this->cache[$name] = new Config($name, $this->storage, $this->eventDispatcher);
+    return $this->cache[$name]->init();
   }
 
   /**
-   * Reset config objects. Internal only.
+   * Resets and re-initializes configuration objects. Internal use only.
    *
    * @param string $name
-   *   The name of the object to reset. If NULL then all objects are reset.
+   *   (optional) The name of the configuration object to reset. If omitted, all
+   *   configuration objects are reset.
    */
-  public function resetConfig($name = NULL) {
+  public function reset($name = NULL) {
     if ($name) {
-      if (isset($this->configs[$name])) {
-        $this->configs[$name]->init();
+      if (isset($this->cache[$name])) {
+        $this->cache[$name]->init();
       }
     }
     else {
-      foreach ($this->configs as $config) {
+      foreach ($this->cache as $config) {
         $config->init();
       }
     }
   }
 
   /**
-   * @todo: remove after http://drupal.org/node/1865206.
+   * Renames a configuration object in the cache.
+   *
+   * @param string $old_name
+   *   The old name of the configuration object.
+   * @param string $new_name
+   *   The new name of the configuration object.
    *
-   * @param $old_name
-   * @param $new_name
+   * @todo D8: Remove after http://drupal.org/node/1865206.
    */
-  public function renameConfig($old_name, $new_name) {
-    // This will likely always be TRUE
-    if (isset($this->configs[$old_name])) {
-      $config = $this->configs[$old_name];
-      // Save a clone of the config object in the old slot
-      $this->configs[$old_name] = clone $config;
+  public function rename($old_name, $new_name) {
+    if (isset($this->cache[$old_name])) {
+      $config = $this->cache[$old_name];
+      // Clone the object into the existing slot.
+      $this->cache[$old_name] = clone $config;
 
-      // Update the name and re-init the object
-      // then save it in the slot of the new_name
+      // Change the object's name and re-initialize it.
       $config->setName($new_name)->init();
-      $this->configs[$new_name] = $config;
+      $this->cache[$new_name] = $config;
     }
   }
 }
diff -u b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
--- b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigStorageController.php
@@ -289,12 +289,12 @@
     $config = config($prefix . $id);
     $is_new = $config->isNew();
 
-    if ($id != $entity->id()) {
-      // We need to keep three things in mind for a rename:
-      // * Storage controller needs to access the original object
-      // * Object should be renamed in ConfigFactory and slot should be updated
-      // * All instances of the Object should be renamed
-      drupal_container()->get('config.factory')->renameConfig($prefix . $id, $prefix . $entity->id());
+    if ($id !== $entity->id()) {
+      // Renaming a config object needs to cater for:
+      // - Storage controller needs to access the original object.
+      // - The object needs to be renamed/copied in ConfigFactory and reloaded.
+      // - All instances of the object need to be renamed.
+      drupal_container()->get('config.factory')->rename($prefix . $id, $prefix . $entity->id());
     }
 
     if (!$is_new && !isset($entity->original)) {
diff -u b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -808,6 +808,7 @@
     global $conf;
     cache('bootstrap')->delete('variables');
     $conf = variable_initialize();
+    drupal_container()->get('config.factory')->reset();
   }
 
   /**
@@ -1227,7 +1228,6 @@
           $out = $this->curlExec(array(CURLOPT_URL => $action, CURLOPT_POST => TRUE, CURLOPT_POSTFIELDS => $post, CURLOPT_HTTPHEADER => $headers));
           // Ensure that any changes to variables in the other thread are picked up.
           $this->refreshVariables();
-          drupal_container()->get('config.factory')->resetConfig();
 
           // Replace original page output with new output from redirected page(s).
           if ($new = $this->checkForMetaRefresh()) {