What's happening is that, while the lemming is in the teleporter, the projectile constantly moves by the amount it would move by on the current frame of the lemming's animation. (It needs to do this, rather than just jumping to fixed positions, as part of the interim terrain detections.) Because the lemming's animation isn't updating (as it's in the teleporter)... well, you can figure the rest. Indeed, if the projectile hasn't hit something by the time the lemming comes out the other side, it should resume the normal path (from its current position at the time, not the lemming's actual position) once the lemming does come out.