Comment 1 for bug 1598469

Further research: the bug affects also enblend (using two vertical halves of the same images as above). With a plus: with enblend I also get other parasite horizontal lines, white with a light blue pixel at the left end, 1px thick and vertically spaced by 32px. They appear in the bottom region of the image, apparently below the 10'000th pixel. See attached image.