This has happened multiple times, but I cannot repeat it at will. The back has been to Denmark 2-3 times to get this fixed, but the problem is still there. Last night, the error appeared twice in two separate focus stacks. It is hard to spot usually, because it might be a single pixel horizontal line, usually white, running through the entire picture horizontally about a third of the way into the frame. The worst I've seen, the line is around eight pixels thick, because there is about three pixels of anti-aliasing on either side of a two pixel center.
So far, I have only seen this with focus stacks, and only see it because putting it through the focus stacking tool makes it easier to see. Once detected, it can be difficult to find the image the error belongs to.
Has anyone else seen this?