DateTime->diff having issues with leap days

[simonwelsh]

HHVM Version

3.24.2

Standalone code, or other way to reproduce the problem

<?php

date_default_timezone_set('UTC');

$d = new DateTime('2008-03-01');
$a = new DateTime('2018-03-01');

var_dump($d->diff($a)->y);

date_default_timezone_set('Europe/Amsterdam');

$d = new DateTime('2008-03-01');
$a = new DateTime('2018-03-01');

var_dump($d->diff($a)->y);

Expected result

int(10)
int(10)

Actual result

int(10)
int(9)

PHP bug report: https://bugs.php.net/bug.php?id=76032