How to combine multiple bitmaps/images with alpha data while keeping RGB values

[floxay]

I'm trying to combine multiple RGBA tiles into one image however due to the alpha channel RGB data seems to be discarded where the alpha is 0 (fully transparent).
Both the target and tile bitmaps have alpha types set to unpremultiplied. The individual tile bitmaps contain the RGB and A data.
Could this be an optimization done on Skia's side under the hood, or maybe a SkiaSharp limitation?
If so, can this be turned off/bypassed without an unsafe context and accessing/modifying the pixel data directly?

Snippet:

var bitmap = new SKBitmap(bitmapWidth, bitmapHeight, SKImageInfo.PlatformColorType, SKAlphaType.Unpremul);
using var canvas = new SKCanvas(bitmap);

for ...
{
	...
	SKBitmap tile = ...  // tile bitmap with SKAlphaType.Unpremul
	canvas.DrawBitmap(tile, tileCrop, new SKRect(x, y, x + tileSize, y + tileSize));  // just cutting off borders
}

Also tried by setting each pixel of the tiles via SetPixel()/DrawPoint() but where the image is fully transparent RGB data still gets discarded and replaced with black.

Externally opened issue with image example: (as I'm unsure whether it's an issue/bug with Skia(Sharp) or this is the expected behavior)
FabianFG/CUE4Parse#147
Full code: https://github.com/FabianFG/CUE4Parse/blob/500670ad0afa308441aca03587e18b437ca6c385/CUE4Parse-Conversion/Textures/TextureDecoder.cs#L99

[floxay]

After some digging I found this: #1142
I'm pretty sure it's the same issue, and looks like it's a bug with no fix currently.

I'm closing this one as a duplicate.