Description:
------------
The documentation for ReflectionProperty::setAccessible() implies that the change should not effect the object property visibility and this is true of user land classes, however DateTime works a bit differently, and doesn't match the behavior around userland classes.

Test script:
---------------
<?php
$subject = new DateTime('2015-06-24 22:09:00');
var_dump(isset($subject->timezone));

$reflection = new ReflectionObject($subject);
foreach ($reflection->getProperties() as $prop) {
    $prop->setAccessible(true);
    $prop->setAccessible(false);
}
var_dump(isset($subject->timezone));

Expected result:
----------------
I would expect the output to be:

bool(false)
bool(false)



Actual result:
--------------
However, it is:

bool(false)
bool(true)