classes/interfaces don't show methods inherited from PHP built-in classes/interfaces

For example, look at https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21...

We have:

interface EntityConstraintViolationListInterface extends ConstraintViolationListInterface {

and in Symfony at https://api.drupal.org/api/drupal/vendor%21symfony%21validator%21Constra... we have:

interface ConstraintViolationListInterface extends \Traversable, \Countable, \ArrayAccess

Yet the count() method isn't showing in the list of methods for either interface.

This could be some sort of parsing glitch, as the page for the Symfony interface says:

interface \Symfony\Component\Validator\ConstraintViolationListInterface extends \Symfony\Component\Validator\Traversable

Has the parser maybe picked up the wrong Traversable interface?