The Dink Network

I don't know how the engine is constructed, I haven't looked at the source code, but maybe dink's movement is dependent on a clock variable to ensure that it runs at about the same speed across all computers. This could lead to dink "jumping" if the computer can't keep up so that the collision isn't tested until he moves through the hardness. This would indeed be more common by the shoreline as the "hard"-area are thinner, just a few pixels.