QImage crash when the format is "Format_Indexed8"

[stereoMatching]

os : win7 64bits
compiler : mingw4.6.2
qt version : qt4.8.1(the dll and and the lib haven't rebuild by mingw4.6.2)

#include <QtGui/QApplication>
#include <QtGui/QImage>
 
int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
 
    QImage src("../GIL_with_Qt/images_00/lena/lena.jpg");
    src = src.convertToFormat(QImage::Format(3) );
    QImage dst(src.size(), src.format());       
 
    dst.save("E:/lena/lena_Format_Indexed8.jpg");
    return a.exec();
}

#include <QtGui/QApplication>
#include <QtGui/QImage>

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);

    QImage src("../GIL_with_Qt/images_00/lena/lena.jpg");
    src = src.convertToFormat(QImage::Format(3) );
    QImage dst(src.size(), src.format());       

    dst.save("E:/lena/lena_Format_Indexed8.jpg");
    return a.exec();
}

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This will cause the program crash, what kind of mistake do I make?
Thank you very much