Re: red bandana: Ah, I see.
Re: hold left bug: Ok for some reason it only works when rendering the game at more than 60 fps (e.g. on a high refresh rate monitor while not in fullscreen mode). If I limit the browser's refresh rate to 60 or below, the bug doesn't happen.
I'm on a >60hz monitor, so I will be checking all the games I've played here to see whether I played any of them at 2x speed due to delta time stuff. Luckily it appears that this game handled it properly, with the exception of this bug and maybe some minor stuff that I couldn't find.