Mouse not locked to window

[horribad]

Have a dual monitor setup and when I scroll my mouse cursor to the side in a game like League of Legends the mouse will move into my other screen (to the left) - essentially it's not locked into that specific window.

I've tried playing in windowed, borderless window and full screen. Nothing changes.

I'm on Windows 8.1. Any advice would be great.

 

[horribad]

I've figured out that for some reason if I pan my cursor slow enough it doesn't go to the other screen. If I do it quickly, however, it will move to the other screen. Any way to disable this?

 

[horribad]

Still not found a solution to this. Any advice?