Description:
------------
i use php library "Carbon/Carbon" witch use DateTime directly 
and when i add one day to this exact day "2016-03-20" with timezone of "Asia/Tehran" it give one extra hour
but when i add two day it works just fine.

Test script:
---------------
$timezone = new DateTimeZone('Asia/Tehran');
$dayStart = new DateTime('2016-03-20 00:00:00.000000', $timezone);

$dayOne = (new DateTime('2016-03-20 00:00:00.000000', $timezone))->modify('1 day');
$dayTwo = (new DateTime('2016-03-20 00:00:00.000000', $timezone))->modify('2 day');


echo json_encode([
    '$dayStart' => $dayStart,
    '$dayOne' => $dayOne,
    'diff of $dayOne' => $dayStart->diff($dayOne,true),
    '$dayTwo' => $dayTwo,
    'diff of $dayTwo' => $dayStart->diff($dayTwo,true),
]);
die;

Expected result:
----------------
{
    "$dayStart": {
        "date": "2016-03-20 00:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "$dayOne": {
        "date": "2016-03-21 00:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "diff of $dayOne": {
        "y": 0,
        "m": 0,
        "d": 1,
        "h": 0,
        "i": 0,
        "s": 0,
        "weekday": 0,
        "weekday_behavior": 0,
        "first_last_day_of": 0,
        "invert": 0,
        "days": 1,
        "special_type": 0,
        "special_amount": 0,
        "have_weekday_relative": 0,
        "have_special_relative": 0
    },
    "$dayTwo": {
        "date": "2016-03-22 00:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "diff of $dayTwo": {
        "y": 0,
        "m": 0,
        "d": 2,
        "h": 0,
        "i": 0,
        "s": 0,
        "weekday": 0,
        "weekday_behavior": 0,
        "first_last_day_of": 0,
        "invert": 0,
        "days": 2,
        "special_type": 0,
        "special_amount": 0,
        "have_weekday_relative": 0,
        "have_special_relative": 0
    }
}

Actual result:
--------------
{
    "$dayStart": {
        "date": "2016-03-20 00:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "$dayOne": {
        "date": "2016-03-21 01:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "diff of $dayOne": {
        "y": 0,
        "m": 0,
        "d": 1,
        "h": 1,
        "i": 0,
        "s": 0,
        "weekday": 0,
        "weekday_behavior": 0,
        "first_last_day_of": 0,
        "invert": 0,
        "days": 1,
        "special_type": 0,
        "special_amount": 0,
        "have_weekday_relative": 0,
        "have_special_relative": 0
    },
    "$dayTwo": {
        "date": "2016-03-22 00:00:00.000000",
        "timezone_type": 3,
        "timezone": "Asia\/Tehran"
    },
    "diff of $dayTwo": {
        "y": 0,
        "m": 0,
        "d": 2,
        "h": 0,
        "i": 0,
        "s": 0,
        "weekday": 0,
        "weekday_behavior": 0,
        "first_last_day_of": 0,
        "invert": 0,
        "days": 2,
        "special_type": 0,
        "special_amount": 0,
        "have_weekday_relative": 0,
        "have_special_relative": 0
    }
}