You might have misread it. These white artifacts were camouflaged with the white-grey checkered background. It's best to put a black background behind your working image, then remove that background after you've done. This is the method used to detect white artifacts.
In summary: Add a black background layer behind the layer you're working on, then remove that layer after you've done.
In summary: Add a black background layer behind the layer you're working on, then remove that layer after you've done.