I would also argue "it's not a bug, it's a feature" because logically the lemming is still in the Jumper phase when they touch the terrain and haven't entered the Faller state at any point on the examples where they survive. At least for me, it's game logic I can understand and also easy enough to test if a level includes it. I would argue that level designers should probably avoid this set-up to avoid confusion, but that's up to them.