f.lux mostly disables in fullscreen mode but not entirely

[Zoook]

I have f.lux set to disable for full screen apps. When I go fullscreen in my browser, f.lux gets much bluer, and looks like this:
A screenshot in windowed mode looks identical but the screen is much redder. However when I actually disable f.lux, or go into a specific application that f.lux is disabled for, like Microsoft Paint, to paste a screenshot, it seems to actually fully disable, and looks like this:
What can explain the different behavior?

I am on Windows 8.1, f.lux 4.120, my monitor is hooked up to my laptop via a DisplayPort cable.