Description:
------------
---
From manual page: http://www.php.net/intldateformatter.create
---
Passing dates to given function, depending on locale, gives different result

As you can see from few examples below, it returns completely different results depending on locale, which is totally unexpected. I tried finding the cause of it but nothing worked.

Test script:
---------------
    public function reformatDate(\DateTime $date, $format = 'LLLL Y'){
        //make sure the given format exists
        if(!function_exists('datefmt_create')){
            return $date->format('d.m.Y');
        }

        $fmt = datefmt_create(
            'pl_PL', //locale altered in Expected/Actual result part of bug report
            \IntlDateFormatter::FULL,
            \IntlDateFormatter::FULL,
            'Europe/Warsaw',
            \IntlDateFormatter::GREGORIAN,
            $format
        );

        return $fmt->format($date);
    }

Expected result:
----------------
Date | pl_PL | en_EN | pl_PL correct
2015-01-01 | styczen 2015 | january 2015
2015-12-01 | grudzien 2015 | december 2015
2016-01-01 | styczen 2016 | january 2016
2017-01-01 | styczen 2017 | january 2017

Actual result:
--------------
Date | pl_PL | en_EN
2015-01-01 | styczen 2015 | january 2015
2015-12-01 | grudzien 2015 | december 2015
2016-01-01 | styczen 2015 | january 2016
2017-01-01 | styczen 2016 | january 2017