Unexpected Traversable behavior

traversable.php

<?php

echo 'Declaring interface: ';
interface T extends Traversable {}
echo 'OK' . PHP_EOL;

echo 'Abstract class with right interfaces order:';
abstract class A implements Iterator, T {} // OK
echo 'OK' . PHP_EOL;

echo 'Abstract class with wrong interfaces order:';
abstract class B implements T, Iterator {} // Fails
echo 'You will never see this line' . PHP_EOL;