Fixing issue with FieldGroup and its __clone() method not properly setting the parent.

src/Symfony/Component/Form/FieldGroup.php

@@ -57,8 +57,11 @@ class FieldGroup extends Field implements \IteratorAggregate, FieldGroupInterfac
      */
     public function __clone()
     {
-        foreach ($this->fields as $name => $field) {
-            $this->fields[$name] = clone $field;
+        foreach ($this->fields as $name => $field)
+        {
+            $field = clone $field;
+            $field->setParent($this);
+            $this->fields[$name] = $field;
         }
     }