I remember this giving me headaches years ago when I tried to save color data in a PNG with 0-alpha values that contain color. I needed the color and the alpha and thought it would make sense to save both in one image, basically, but nope. This was with GIMP and I remember looking it up and the GIMP devs insisting it was correct behavior by the PNG standard even when it made oh-so-much sense to at least give an option to bypass this shit for niche cases.
fought with this recently while creating pdf having image overlays, ended up having to draw the underlining image on top image's pixel having full alpha to avoid aliasing on the edges
