QXmlStreamWriter breaks while trying to use non-utf8 encoding

#include <QCoreApplication>
#include <QXmlStreamWriter>
#include <QFile>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QString s = "α фетопротеин"; // utf-8 string
    qDebug().noquote() << s << endl;


    QFile file("bug.xml");
    if(!file.open(QIODevice::Text | QIODevice::WriteOnly))
        return -1;

    QXmlStreamWriter sw(&file);
    sw.setAutoFormatting(true);
    sw.setAutoFormattingIndent(-1);
    sw.setCodec("WINDOWS-1251");
    sw.writeStartDocument("1.0");
    sw.writeStartElement("ROOT");
    sw.writeAttribute("CORRECT", QString::fromLocal8Bit(s.toLocal8Bit())); // replaces "α" character with "?"
    sw.writeAttribute("BUGGED", s);  // should be ? mark instead of "α" character but it is "" and from now on every other tag/attribute looks like ="" and <></>

    for(int i = 0; i < 3; i++)
    {
        sw.writeStartElement("SUBTAG");
        sw.writeAttribute("BUGGED2", s);

        for(int j = 0; j < 3; j++)
        {
            sw.writeStartElement("SUBTAG_TOO");
            sw.writeAttribute("BUGGED_TOO", "correct ansi string");
            sw.writeEndElement();
        }

        sw.writeEndElement();
    }

    sw.writeEndElement(); // ROOT
    sw.writeEndDocument();
    file.close();

    return a.exec();
}

<?xml version="1.0" encoding="windows-1251"?>
<ROOT CORRECT="? фетопротеин" BUGGED="">
	< ="">
		< =""/>
		< =""/>
		< =""/>
	</>
	< ="">
		< =""/>
		< =""/>
		< =""/>
	</>
	< ="">
		< =""/>
		< =""/>
		< =""/>
	</>
</>