It isn't really a bug, it is just the frequency at which the collisions are calculated. Let's say the collision detection runs at 100Hz. That means that every 10ms, LFS checks to see if you have collided into a surface. But, in 10ms you may have moved enough distance that you are already imside the wall when the collisons are calculated. If you were going 200 m/s, then you might fly though the wall as if it is not even there!