Description:
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I use an object {DateTime} for mass generation intervals in the database. When generating discovered a serious error. By moving the dates in 1 month I have not received February 2017

Test script:
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$lastDate = new DateTime();
$lastDate->sub(new DateInterval("P1M"));

$generateToThisDate = new DateTime();
$generateToThisDate->add(new DateInterval("P20M"));

while ($lastDate < $generateToThisDate) {
  $lastDate->add(new DateInterval("P1M"));
  echo $lastDate->format('Y-m-01') . " - " . $lastDate->format('Y-m-t') . "\n";
}


Expected result:
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list of new dates:
2016-05-01 - 2016-05-31
2016-06-01 - 2016-06-30
2016-07-01 - 2016-07-31
2016-08-01 - 2016-08-31
2016-09-01 - 2016-09-30
2016-10-01 - 2016-10-31
2016-11-01 - 2016-11-30
2016-12-01 - 2016-12-31
2017-01-01 - 2017-01-31
2017-03-01 - 2017-03-31
2017-04-01 - 2017-04-30
2017-05-01 - 2017-05-31
2017-06-01 - 2017-06-30
2017-07-01 - 2017-07-31
2017-08-01 - 2017-08-31
2017-09-01 - 2017-09-30
2017-10-01 - 2017-10-31
2017-11-01 - 2017-11-30
2017-12-01 - 2017-12-31
2018-01-01 - 2018-01-31
2018-02-01 - 2018-02-28
2018-03-01 - 2018-03-31
2018-04-01 - 2018-04-30
2018-05-01 - 2018-05-31
2018-06-01 - 2018-06-30

Actual result:
--------------
list of new dates:
2016-05-01 - 2016-05-31
2016-06-01 - 2016-06-30
2016-07-01 - 2016-07-31
2016-08-01 - 2016-08-31
2016-09-01 - 2016-09-30
2016-10-01 - 2016-10-31
2016-11-01 - 2016-11-30
2016-12-01 - 2016-12-31
2017-01-01 - 2017-01-31
2017-02-01 - 2017-02-28
2017-03-01 - 2017-03-31
2017-04-01 - 2017-04-30
2017-05-01 - 2017-05-31
2017-06-01 - 2017-06-30
2017-07-01 - 2017-07-31
2017-08-01 - 2017-08-31
2017-09-01 - 2017-09-30
2017-10-01 - 2017-10-31
2017-11-01 - 2017-11-30
2017-12-01 - 2017-12-31
2018-01-01 - 2018-01-31
2018-02-01 - 2018-02-28
2018-03-01 - 2018-03-31
2018-04-01 - 2018-04-30
2018-05-01 - 2018-05-31
2018-06-01 - 2018-06-30