HHVM and PHP usort difference

hhvm-usort.php

<?php

class T {
	public function __construct($v)
	{
		$this->v = $v;
	}
	public function __toString()
	{
		return 'a';
	}
}

$list = [new T(1), new T(2)];

usort($list, function($a, $b) {
	return strcmp($a, $b);
});

// PHP reverses $list but HHVM doesn't touch it
print_r($list);