diff --git a/core/lib/Drupal/Core/Field/FieldItemBase.php b/core/lib/Drupal/Core/Field/FieldItemBase.php
index 3eb6b4e..1dd8bf8 100644
--- a/core/lib/Drupal/Core/Field/FieldItemBase.php
+++ b/core/lib/Drupal/Core/Field/FieldItemBase.php
@@ -105,10 +105,7 @@ protected function getSetting($setting_name) {
   }
 
   /**
-   * Overrides \Drupal\Core\TypedData\TypedData::setValue().
-   *
-   * @param array|null $values
-   *   An array of property values.
+   * {@inheritdoc}
    */
   public function setValue($values, $notify = TRUE) {
     // Treat the values as property value of the first property, if no array is
@@ -117,20 +114,7 @@ public function setValue($values, $notify = TRUE) {
       $keys = array_keys($this->definition->getPropertyDefinitions());
       $values = array($keys[0] => $values);
     }
-    $this->values = $values;
-    // Update any existing property objects.
-    foreach ($this->properties as $name => $property) {
-      $value = NULL;
-      if (isset($values[$name])) {
-        $value = $values[$name];
-      }
-      $property->setValue($value, FALSE);
-      unset($this->values[$name]);
-    }
-    // Notify the parent of any changes.
-    if ($notify && isset($this->parent)) {
-      $this->parent->onChange($this->name);
-    }
+    parent::setValue($values, $notify);
   }
 
   /**
@@ -139,33 +123,32 @@ public function setValue($values, $notify = TRUE) {
   public function __get($name) {
     // There is either a property object or a plain value - possibly for a
     // not-defined property. If we have a plain value, directly return it.
-    if (isset($this->values[$name])) {
-      return $this->values[$name];
-    }
-    elseif (isset($this->properties[$name])) {
+    if (isset($this->properties[$name])) {
       return $this->properties[$name]->getValue();
     }
+    elseif (isset($this->values[$name])) {
+      return $this->values[$name];
+    }
   }
 
   /**
-   * {@inheritdoc}
+   * Writes the value of a property without handling changes.
+   *
+   * @param string $property_name
+   *   The name of the property to be written.
+   * @param $value
+   *   The value to set.
    */
-  public function set($property_name, $value, $notify = TRUE) {
+  protected function writePropertyValue($property_name, $value) {
     // For defined properties there is either a property object or a plain
     // value that needs to be updated.
     if (isset($this->properties[$property_name])) {
       $this->properties[$property_name]->setValue($value, FALSE);
-      unset($this->values[$property_name]);
     }
     // Allow setting plain values for not-defined properties also.
     else {
       $this->values[$property_name] = $value;
     }
-    // Directly notify ourselves.
-    if ($notify) {
-      $this->onChange($property_name);
-    }
-    return $this;
   }
 
   /**
@@ -184,7 +167,10 @@ public function __set($name, $value) {
    * {@inheritdoc}
    */
   public function __isset($name) {
-    return isset($this->values[$name]) || (isset($this->properties[$name]) && $this->properties[$name]->getValue() !== NULL);
+    if (isset($this->properties[$name])) {
+      return $this->properties[$name]->getValue() !== NULL;
+    }
+    return isset($this->values[$name]);
   }
 
   /**
@@ -202,21 +188,6 @@ public function __unset($name) {
   }
 
   /**
-   * Overrides \Drupal\Core\TypedData\Map::onChange().
-   */
-  public function onChange($property_name) {
-    // Notify the parent of changes.
-    if (isset($this->parent)) {
-      $this->parent->onChange($this->name);
-    }
-    // Remove the plain value, such that any further __get() calls go via the
-    // updated property object.
-    if (isset($this->properties[$property_name])) {
-      unset($this->values[$property_name]);
-    }
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function view($display_options = array()) {
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
index 317befd..31dac70 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -140,14 +140,10 @@ public static function schema(FieldStorageDefinitionInterface $field_definition)
    * {@inheritdoc}
    */
   public function setValue($values, $notify = TRUE) {
+    // Treat the values as property value of the entity property, if no array
+    // is given as this handles entity ids and objects.
     if (isset($values) && !is_array($values)) {
-      // Directly update the property instead of invoking the parent, so it can
-      // handle objects and IDs.
-      $this->properties['entity']->setValue($values, $notify);
-      // If notify was FALSE, ensure the target_id property gets synched.
-      if (!$notify) {
-        $this->set('target_id', $this->properties['entity']->getTargetIdentifier(), FALSE);
-      }
+      $this->set('entity', $values, $notify);
     }
     else {
       // Make sure that the 'entity' property gets set as 'target_id'.
@@ -176,22 +172,14 @@ public function getValue($include_computed = FALSE) {
    * {@inheritdoc}
    */
   public function onChange($property_name, $notify = TRUE) {
-    // Let the parent class do its work first, such that $this->values and
-    // $this->properties are in sync.
-    parent::onChange($property_name, FALSE);
-
     // Make sure that the target ID and the target property stay in sync.
     if ($property_name == 'target_id') {
-      $this->properties['entity']->setValue($this->target_id, FALSE);
+      $this->writePropertyValue('entity', $this->target_id);
     }
     elseif ($property_name == 'entity') {
-      $this->set('target_id', $this->properties['entity']->getTargetIdentifier(), FALSE);
-    }
-
-    // Notify the parent of changes.
-    if (isset($this->parent) && $notify) {
-      $this->parent->onChange($this->name);
+      $this->writePropertyValue('target_id', $this->get('entity')->getTargetIdentifier());
     }
+    parent::onChange($property_name, $notify);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
index 7d0329b..851b818 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/LanguageItem.php
@@ -69,14 +69,7 @@ public function setValue($values, $notify = TRUE) {
     // Treat the values as property value of the language property, if no array
     // is given as this handles language codes and objects.
     if (isset($values) && !is_array($values)) {
-      // Directly update the property instead of invoking the parent, so that
-      // the language property can take care of updating the language code
-      // property.
-      $this->properties['language']->setValue($values, $notify);
-      // If notify was FALSE, ensure the value property gets synched.
-      if (!$notify) {
-        $this->set('value', $this->properties['language']->getTargetIdentifier(), FALSE);
-      }
+      $this->set('language', $values, $notify);
     }
     else {
       // Make sure that the 'language' property gets set as 'value'.
@@ -101,22 +94,14 @@ public function applyDefaultValue($notify = TRUE) {
    * {@inheritdoc}
    */
   public function onChange($property_name, $notify = TRUE) {
-    // Let the parent class do its work first, such that $this->values and
-    // $this->properties are in sync.
-    parent::onChange($property_name, FALSE);
-
     // Make sure that the value and the language property stay in sync.
     if ($property_name == 'value') {
-      $this->properties['language']->setValue($this->value, FALSE);
+      $this->writePropertyValue('language', $this->value);
     }
     elseif ($property_name == 'language') {
-      $this->set('value', $this->properties['language']->getTargetIdentifier(), FALSE);
-    }
-
-    // Notify the parent of changes.
-    if (isset($this->parent) && $notify) {
-      $this->parent->onChange($this->name);
+      $this->writePropertyValue('value', $this->get('language')->getTargetIdentifier());
     }
+    parent::onChange($property_name, $notify);
   }
 
 }
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
index 408c0cc..374d083 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
@@ -134,21 +134,32 @@ public function get($property_name) {
   }
 
   /**
-   * Implements \Drupal\Core\TypedData\ComplexDataInterface::set().
+   * {@inheritdoc}
    */
   public function set($property_name, $value, $notify = TRUE) {
+    // Separate the writing in a protected method, such that onChange
+    // implementations can make use of it.
+    $this->writePropertyValue($property_name, $value);
+    $this->onChange($property_name, $notify);
+    return $this;
+  }
+
+  /**
+   * Writes the value of a property without handling changes.
+   *
+   * @param string $property_name
+   *   The name of the property to be written.
+   * @param $value
+   *   The value to set.
+   */
+  protected function writePropertyValue($property_name, $value) {
     if ($this->definition->getPropertyDefinition($property_name)) {
-      $this->get($property_name)->setValue($value, $notify);
+      $this->get($property_name)->setValue($value, FALSE);
     }
     else {
       // Just set the plain value, which allows adding a new entry to the map.
       $this->values[$property_name] = $value;
-      // Directly notify ourselves.
-      if ($notify) {
-        $this->onChange($property_name, $value);
-      }
     }
-    return $this;
   }
 
   /**