When alpha blending some greyscale images on Win7 x64 I m getting strange tearing and flicker. It s fine on XP & Vista (both x64 and x86) and Win7 x86. I ve tried it on several Win7 machines, and they all show the problem.

The code that shows up the problem is:

public partial class Form1 : Form
{
    Image image;
    float alpha = 0;
    float delta = 0.1f;
    Timer timer;

    public Form1()
    {
        InitializeComponent();
        DoubleBuffered = true;
        Paint += Form1_Paint;

        image = Image.FromFile(@"image.jpg");

        timer = new Timer {Interval = 50};
        timer.Tick += timer_Tick;
        timer.Start();
    }

    void timer_Tick(object sender, EventArgs e)
    {
        if (alpha > 1 || alpha < 0)
        {
            delta = -delta;
        }

        alpha += delta;
        Invalidate();
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        e.Graphics.FillRectangle(Brushes.White, new Rectangle(0, 0, image.Width, image.Height));
        float[][] matrix = {
                                    new float[] {1, 0, 0, 0, 0},
                                    new float[] {0, 1, 0, 0, 0},
                                    new float[] {0, 0, 1, 0, 0},
                                    new float[] {0, 0, 0, alpha, 0},
                                    new float[] {0, 0, 0, 0, 1}
                                 };
        var colorMatrix = new ColorMatrix(matrix);

        using (var attributes = new ImageAttributes())
        {
            attributes.SetColorMatrix(colorMatrix,
                                         ColorMatrixFlag.Default,
                                         ColorAdjustType.Bitmap);
            e.Graphics.DrawImage(image,
                               new Rectangle(0, 0, image.Width, image.Height),
                               0, 0, image.Width, image.Height,
                               GraphicsUnit.Pixel, attributes);
        }   
    }


}

(this is part of default Windows Form project)

The image that shows the problem is:

Am I doing something wrong with my ColorMatrix code? Or is this one of those rare cases where I may have found a problem in the Framework/OS/whatever I m building on top of?