That's not a software bug, that's an image retention issue with your monitor. If it was that severe then it probably got into a state where it was sending severely invalid timings to the TFT LCD array, DC biasing it, which causes long-term retention and may even cause permanent damage if done for too long.
Software isn't supposed to be able to cause that. That's on your monitor.
I _think_ it was every other frame, and I am fairly sure that it was a software/driver issue. It had never happened before, it has not happened since, and it started immediately when starting the game and the symptoms got progressively worse and triggering the mild symptoms happened every time I started the game.
What I convinced myself of after a few minutes being sure I wasn't hallucinating was that the graphics driver was pushing out malformed data in some way or the other which was triggering bugs in the monitor hardware/firmware, which is easy to believe are plentiful. It would be an interesting project to try to track down and replicate the bug.
Software isn't supposed to be able to cause that. That's on your monitor.