Qyoto problem using oxygen/qtcurve theme

using System;
using QtCore;
using QtGui;

namespace qtcoretest
{
    public class QyotoApp: QWidget
    {

        [STAThread]
        public static int Main(string[] args)
        {
            new QApplication(args);
            new QyotoApp();
            return QApplication.Exec();
        }


        [Q_SLOT]
        private void OpenDialog()
        {
            QFileDialog.GetOpenFileName (this, "test open file dialog", null, "*.*");
        }

        public QyotoApp()
        {
            WindowTitle = "QtCore Test";
            Resize(250, 150);
            Move(300, 300);

            QPushButton quit = new QPushButton("Open File Dialog", this);
            Connect(quit, SIGNAL("clicked()"), this, SLOT("OpenDialog()"));
            quit.SetGeometry(50, 40, 160, 50);

            Show();
        }

    }
}