I was enjoying this game. In a lot of ways it re-imagines the idea of platforming.
But I've hit a strange bug: on level 18, there is a steady stream of bullets coming out of the gap in the wall above the key. The level is un-winnable this way. I checked the walkthrough, in it these bullets are not there. Was the game hacked?
I'll try reloading, but I'm not sure it will help.