Severe aspect ratio issues on boot- unable to access menus.

[mdiggler.michts]

For background, I'm running a dual monitor 1920x1080p setup in Windows 10. Never seen this kind of issue before.
When I boot Deadlock, the game window rapidly stretches upwards infinitely such that UI elements become inaccessible.
Actual program capture (game open for ~15 seconds):

 

[mdiggler.michts]

update: putting -fullscreen in boot options seems to have fixed the issue. unsure why windowed breaks it so badly.