silverstripe-framework-4993.php

public function updateFilesystem() {
  $filenameBeforeUpdate = $this->Filename;

  parent::updateFilesystem();

  if($filenameBeforeUpdate != $this->Filename){
    // in this case the filename has changed due to a changed parent
    // we need to write the change to the db, otherwise the children won't see it
    $this->write();
    // no need to proceed as this method has already been called again by the write above
    return; 
  }

  // unmodified from here on
  if($this->ID && ($children = $this->AllChildren())) {
    foreach($children as $child) {
      $child->updateFilesystem();
      $child->write(); // might be only necessary if it is a file?
    }
  }
}