Wow, thanks!
The key the input effect binds to is determined by the key you press to enter the charging area. So if you move left to enter the charge area, the left key will be assigned with the effect - removing that effect from any other keys.
I don't really want to explain how this works to players in-game - working out how the old machine works is half the game! So I'm trying to work out a way to teach the players with some silent tutorials... I think some of the new areas I've made for the game will help with this. They're a little more linear to begin with and introduce mechanics and ideas at a bit more of a staggered pace.