I had the user press space to start playing the game, which then switched to the play scene, but space was also the controls for aiming and shooting, so no matter what, the space bar would trigger the aiming action in the play state. So, instead of messing around with cancelling input listeners and events and things, I just ignored the first key-up event for spacebar when the play scene loads.
Here is my game: https://itch.io/jam/gmtk-2019/rate/461622