Ok, thank you a lot for playing! The box being there is not a bug, but we should probably have taught the player how to do that trick. It's a fancy result of how the controls were made and it resulted into having a fancy quirk of if you press flip polarity and jump at the same time, you can pass through one way platforms and land on the opposite side. And the enemies appear after you respawn, which when we expand this game, we'll probably make something to make it clear that's what happened.
Anyways, thanks a lot for your feedback, this is our second game and we are indeed planning on expanding this one once the jam is over.