I think this is caused by the same underlying issue as this bug: when hitting a surface it can sometimes stop with a small gap, since it stops as soon as the next step (which at high speeds is a visible distance) goes in to a solid. However with a lower acceleration, it then starts accelerating in to the small gap, and then hits the solid again leaving a smaller gap, which it can then accelerate in to again... this causes the "blinking" effect as it alternates between moving and stopped.
I've fixed the other bug for the next build so it stops within 1px of the obstacle it hit. Since this eliminates the gap and there's nothing to accelerate in to, it seems to also fix this issue as well. So it should be working in r248.