Impatient Idealist

I thought about the cheating, and it might be a coding bogon instead of an intentional effect. If they move the pixie some distance (d) on each step and then check for collisios in the x and y planes separately, and flip direction on both collisions if both trigger, as d gets large they'll get more and more bouncing off of sharp corners (something that would happen only infinitesimally often in the Real World TM.)