Description:
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If you subtract timezones from the different sides of the standard/dst time boundary - the result is wrong.

Test script:
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<?php

$dt = new \DateTime('2018-04-01 03:10:00', new \DateTimeZone('Pacific/Auckland'));

$dt2 = clone $dt;
$dt2->sub(new \DateInterval('PT2H'));

var_dump($dt > $dt2, $dt->format(\DateTime::RFC3339), $dt2->format(\DateTime::RFC3339), $dt->diff($dt2)->format('%h'));

Expected result:
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bool(true)
string(25) "2018-04-01T03:10:00+12:00"
string(25) "2018-04-01T02:10:00+13:00"
string(1) "2"

Actual result:
--------------
bool(true)
string(25) "2018-04-01T03:10:00+12:00"
string(25) "2018-04-01T02:10:00+13:00"
string(1) "1"