HYDRATE_ARRAY_HIERARCHY does not return array (returns Doctrine_Collection)

// The Category table is a typical NestedSet of shopping categories (definition below)
$categories = Doctrine_Core::getTable('Category')
  ->findByDql('name LIKE ? OR name LIKE ?', array("$q%", "% $q%"), Doctrine_Core::HYDRATE_RECORD_HIERARCHY);

// This should return bool(true), but returns bool(false)
echo var_dump(is_array($categories));

// This should return null, but returns Doctrine_Collection
echo get_class($categories);

# the category table definition (see attachment for data)
Category:
  actAs:
    NestedSet: { hasManyRoots: true, rootColumnName: root_id }
  columns:
    category_id: { type: integer, unsigned: true, primary: true, autoincrement: true }
    name: { type: string(100), notnull: true }
    description: clob