The issue is in this due the shading being done with a regular matrix of squares in two colors in classic newsprint style. It leads to two problems:
- At small scale, the matrix dimensions do not evenly divide into the screen pix available. The rendering algorithms try their imperfect best, but an uneven shading results (including the gradient towards the darker border lines). That's exactly what you have here (as you can see be zooming to different scales and examine with a magnifying glass). When you scroll, the shading divisions change as the shading grid moves over the pixel grid and the math resolving the fit comes up with different answers (actually nothing to do with screen response times.. it is a classic stroboscopic effect). Once you zoom out to the point that there is no detectible issue in drawing the shading grid within the pixel grid, the effect stops.
- But at that point, you run into another problem.. The Herman grid illusion - which is interesting but probably not what you want your users focused on;-)
If you avoid shading with regular patterns and a small palette you shouldn't have the problem.
Regarding the flickering red, I'm not so sure as I don't see that on my screen. That aspect may be a technical idiosynchrasy of your display or graphics card/driver trying to deal with shading the grid.