Artifacts on translucent WritableBitmap

I drawed translucent WritableBitmap on Bitmap with alpha channel and catched some interesting artifacts. This problem reproduce on Skia and Win32, on Direct2D1 is OK.

View:

<Grid>
    <Image Source="{Binding Bitmap}" />
    <Image Source="{Binding Background}" />
</Grid>

ViewModel:

Background = new Bitmap(PATH_TO_BACKGROUND_FILE);

var data = new byte[256 * 256 * 4];
for (int y = 0; y < 256; y++) {
    for (int x = 0; x < 256; x++) {
        var pos = (y * 256 + x) * 4;
        data[pos] = 255;
        data[pos + 1] = 255;
        data[pos + 2] = 255;
        data[pos + 3] = 1;
    }
}

var writeableBitmap = new WriteableBitmap(256, 256, PixelFormat.Rgba8888);
using (var l = writeableBitmap.Lock()) {
    for (var r = 0; r < 256; r++) {
        Marshal.Copy(data, r * l.RowBytes, new IntPtr(l.Address.ToInt64() + r * l.RowBytes), l.RowBytes);
    }
}

WritableBitmap = writeableBitmap;

Background for example

[ahopper]

I believe this is the same problem as https://github.com/AvaloniaUI/Avalonia/issues/2604 and that the alpha needs pre-multiplying for the WriteableBitmap. This is with pre mmultiplied alpha:-

[kekekeks]

https://github.com/AvaloniaUI/Avalonia/blob/f0a8e64189c7bf60ce7486a35e4a0a67ca644d18/src/Windows/Avalonia.Direct2D1/PrimitiveExtensions.cs#L99 we are using Format32bppPBGRA and Format32bppPRGBA pixel formats. Direct2D might be doing some preprocessing after image bits are unlocked.