diff -u b/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
--- b/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2458,9 +2458,9 @@
     $container->register('config.storage', 'Drupal\Core\Config\DatabaseStorage')
       ->addArgument('%config.storage.options%');
 
-    $container->register('config.globaloverridesubscriber', 'Drupal\Core\EventSubscriber\ConfigGlobalOverrideSubscriber');
+    $container->register('config.subscriber.globalconf', 'Drupal\Core\EventSubscriber\ConfigGlobalOverrideSubscriber');
     $container->register('dispatcher', 'Symfony\Component\EventDispatcher\EventDispatcher')
-      ->addMethodCall('addSubscriber', array(new Reference('config.globaloverridesubscriber')));
+      ->addMethodCall('addSubscriber', array(new Reference('config.subscriber.globalconf')));
     // Register configuration object factory.
     $container->register('config.factory', 'Drupal\Core\Config\ConfigFactory')
       ->addArgument(new Reference('config.storage'))
reverted:
--- b/core/includes/config.inc
+++ a/core/includes/config.inc
@@ -65,7 +65,7 @@
  *   A configuration object.
  */
 function config($name) {
+  return drupal_container()->get('config.factory')->get($name)->load();
-  return drupal_container()->get('config.factory')->get($name);
 }
 
 /**
@@ -195,6 +195,7 @@
       $handled_by_module = FALSE;
       if (module_hook($module, 'config_import_' . $op)) {
         $old_config = new Config($name, $target_storage);
+        $old_config->load();
 
         $data = $source_storage->read($name);
         $new_config = new Config($name, $target_storage);
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
@@ -108,7 +108,6 @@
    * Returns whether this configuration object is new.
    */
   public function isNew() {
-    $this->build();
     return $this->isNew;
   }
 
@@ -140,7 +139,9 @@
    *   The data that was requested.
    */
   public function get($key = '') {
-    $this->build();
+    if (!isset($this->overriddenData)) {
+      $this->setOverriddenData();
+    }
     if (empty($key)) {
       return $this->overriddenData;
     }
@@ -164,7 +165,8 @@
    */
   public function setData(array $data) {
     $this->data = $data;
-    return $this->rebuild();
+    $this->resetOverriddenData();
+    return $this;
   }
 
   /**
@@ -177,7 +179,32 @@
    */
   public function setOverride(array $data) {
     $this->overrides = $data;
-    return $this->rebuild();
+    $this->resetOverriddenData();
+    return $this;
+  }
+
+  /**
+   * Sets the current data for this configuration object.
+   *
+   * Merges overridden configuration data into the original data.
+   */
+  protected function setOverriddenData() {
+    $this->overriddenData = $this->data;
+    if (!empty($this->overrides)) {
+      $this->overriddenData = NestedArray::mergeDeepArray(array($this->overriddenData, $this->overrides));
+    }
+    return $this;
+  }
+
+  /**
+   * Resets the current data, so overrides are re-applied.
+   *
+   * This method should be called after the original data or the overridden data
+   * has been changed.
+   */
+  protected function resetOverriddenData() {
+    unset($this->overriddenData);
+    return $this;
   }
 
   /**
@@ -189,7 +216,6 @@
    *   @todo
    */
   public function set($key, $value) {
-    $this->build();
     // Type-cast value into a string.
     $value = $this->castValue($value);
 
@@ -202,7 +228,8 @@
     else {
       NestedArray::setValue($this->data, $parts, $value);
     }
-    return $this->rebuild();
+    $this->resetOverriddenData();
+    return $this;
   }
 
   /**
@@ -251,7 +278,6 @@
    *   Name of the key whose value should be unset.
    */
   public function clear($key) {
-    $this->build();
     $parts = explode('.', $key);
     if (count($parts) == 1) {
       unset($this->data[$key]);
@@ -259,7 +285,8 @@
     else {
       NestedArray::unsetValue($this->data, $parts);
     }
-    return $this->rebuild();
+    $this->resetOverriddenData();
+    return $this;
   }
 
   /**
@@ -276,19 +303,18 @@
       $this->setData($data);
     }
     $this->notify('load');
-    return $this->rebuild();
+    return $this;
   }
 
   /**
    * Saves the configuration object.
    */
   public function save() {
-    $this->build();
     $this->sortByKey($this->data);
     $this->storage->write($this->name, $this->data);
     $this->isNew = FALSE;
     $this->notify('save');
-    return $this->rebuild();
+    return $this;
   }
 
   /**
@@ -318,41 +344,12 @@
     $this->data = array();
     $this->storage->delete($this->name);
     $this->isNew = TRUE;
+    $this->resetOverriddenData();
     $this->notify('delete');
-    return $this->rebuild();
-  }
-
-  /**
-   * Build the data for this configuration object.
-   *
-   * Loads the base data if not loaded, and builds the overriddenData runtime
-   * configuration computing the overridden values.
-   */
-  public function build() {
-    if (!isset($this->overriddenData)) {
-      if (!isset($this->data)) {
-        $this->load();
-      }
-      $this->overriddenData = $this->data;
-      if (!empty($this->overrides)) {
-        $this->overriddenData = NestedArray::mergeDeepArray(array($this->overriddenData, $this->overrides));
-      }
-    }
     return $this;
   }
 
   /**
-   * Resets the current data, so overrides are re-applied.
-   *
-   * This method should be called after the original data or the overridden data
-   * has been changed.
-   */
-  public function rebuild() {
-    unset($this->overriddenData);
-    return $this->build();
-  }
-
-  /**
    * Retrieve the storage used to load and save this configuration object.
    */
   public function getStorage() {