Description:
------------
All PHP versions affected: 5.6.0 - 5.6.30, 7.0.0 - 7.1.2

- create DateTimeImmutable in UTC, hour before the actual DST switch
- change its timezone to Europe/Prague that observes DST
- absolute date/time stays the same, UTC offset is correctly changed
- call getTimeZone() on the instance
- the offset moves as if it went past the DST switch

Might be related to https://bugs.php.net/bug.php?id=65502

Online test script: https://3v4l.org/pQaKo

Expected:

2016-10-30T02:00:00+02:00
2016-10-30T02:00:00+02:00

Actual:

2016-10-30T02:00:00+02:00
2016-10-30T02:00:00+01:00


Test script:
---------------
<?php

$utc = new \DateTimeImmutable('2016-10-30T00:00:00+00:0');
// reproduces too:
// $utc = new \DateTimeImmutable('2016-10-30T00:00:00', new \DateTimeZone('UTC'));
// $utc = new \DateTimeImmutable('2016-10-30T00:00:00+00:0');

$prg = $utc->setTimeZone(new \DateTimeZone('Europe/Prague'));
echo $prg->format('c') . "\n";
$prg->getTimestamp();
echo $prg->format('c') . "\n";

Expected result:
----------------
2016-10-30T02:00:00+02:00
2016-10-30T02:00:00+02:00


Actual result:
--------------
2016-10-30T02:00:00+02:00
2016-10-30T02:00:00+01:00