SvgDocument Background color not rendered properly

[itanex]

Expected:

Background color renders White (#FFFFFF) as per the SVG specifications.

When an SVG document is a top-level document, meaning it is not embedded in another document, the root ‘svg’ element is considered to be the page group and is composited with a backdrop of white with 100% opacity. From https://www.w3.org/TR/SVG2/render.html#ParentCompositing

Actual:

Background renders transparent.

---

I have tried several attempts to get a white background. Is there something I am missing from the API? Here is my current solution that gets me the white background as I expect, however, this feels like it should be part of the Draw method to comply with the SVG spec.

var bitmap = new Bitmap(
        (int)self.ViewBox.Width,
        (int)self.ViewBox.Height,
        PixelFormat.Format32bppArgb);
            
using (var g = Graphics.FromImage(bitmap))
{
    g.FillRegion(Brushes.White, new Region(new Rectangle(0, 0, bitmap.Width, bitmap.Height)));
}
            
self.Draw(bitmap);

return bitmap;

[H1Gdev]

Is there a description in SVG1.1 about background color ?