Strange flickering using ImageAttributes ColorMatrix in .NET on Win7 x64

Question

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:

I am 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?