Version 4.55 window won't close
I launch f.lux manually; I don't let it start with Windows. When I launch f.lux and then switch back to the window I was working with, it seems the f.lux window never closes like it should. I've seen even a few hours go by before I'll notice it's still open. The only way to get to close automatically is to put focus back onto the f.lux window and then swtich back to whatever I was doing.
I think it started with version 4.55, but I'm not 100% sure.