Space Invaders Plus level progression?

[CaptainBit]

I picked up Space Invaders Plus a while back and I've really enjoyed it thus far. I'm wanting to do a review of it, except for the fact that I have no idea how level progression works.

I've noticed that if you die and then complete a level, you get taken to a different level than if you were to beat the level without dying. Is this how the game works? Or am I triggering something else but just not noticing it?