C# 変換を使用してマウス カーソルからズームすると画像がジャンプするのはなぜですか?

private void trackBar1_Scroll(object sender, EventArgs e) {
    // Get rotation angle
    ang = trackBar1.Value;
    pnl1.Invalidate();
}

private void pnl1_MouseWheel(object sender, MouseEventArgs e) {
    // Get mouse location
    mouse = e.location;

    // Get new scale (zoom) factor
    zoom = (float)(e.Delta > 0 ? zoom * 1.05 : zoom / 1.05);
    pnl1.Invalidate();
}

private void pnl1_MouseDown(object sender, MouseEventArgs e) {
    if (e.Button != MouseButtons.Left) return;
    pan = true;
    mouX = e.X;
    mouY = e.Y;
    oldX = imgX;
    oldY = imgY;
}

private void pnl1_MouseMove(object sender, MouseEventArgs e) {
    if (e.Button != MouseButtons.Left || !pan) return;

    // Coordinates of panned image
    imgX = oldX + e.X - mouX;
    imgY = oldY + e.Y - mouY;
    pnl1.Invalidate();
}

private void pnl1_MouseUp(object sender, MouseEventArgs e) {
    pan = false;
}

private void pnl1_Paint(object sender, PaintEventArgs e) {
    // Apply rotation angle @ center of bitmap
    e.Graphics.TranslateTransform(img.Width / 2, img.Height / 2);
    e.Graphics.RotateTransform(ang);
    e.Graphics.TranslateTransform(-img.Width / 2, -img.Height / 2);

    // Apply scaling factor - focused @ mouse location
    e.Graphics.TranslateTransform(mouse.X, mouse.Y, MatrixOrder.Append);
    e.Graphics.ScaleTransform(zoom, zoom, MatrixOrder.Append);
    e.Graphics.TranslateTransform(-mouse.X, -mouse.Y, MatrixOrder.Append);

    // Apply drag (pan) location
    e.Graphics.TranslateTransform(imgX, imgY, MatrixOrder.Append);

    // Draw "bmp" @ location
    e.Graphics.DrawImage(img, 0, 0);
}