As in the title, I'm having a weird issue with Deadly Shadows.

I tried every setting I could think of yesterday to try and resolve the problem, with no luck.

Specs:

i7 6700K @4.7GHz
GTX 1070
16GB RAM
Windows 10

The game functions correctly before the mod is installed, but when sneaky upgrade is installed (Even if I run the install with no checkboxes ticked), the mouse cursor is no longer prevented from leaving the main game window. This means if I need to turn around to the right and then click on something, I end up clicking somewhere on my second monitor and swapping applications.

I'd ordinarily just disable my second monitor while playing, but I'm hoping to stream the game soon and it would be a bummer to not have a second monitor for chat, etc.

Has anyone encountered this before, and how did they fix it? (Additionally, using the 3rd party program "cursor lock" didn't help)