I've been having this same issue with my dual monitors since .61 experimental started. The same deal, .60 stable doesn't do this and no other games have this issue. I even switched the cables on my screens to my GPU to change which one is Monitor 1 and Monitor 2. .61 Exp always gets put on my left hand screen, I play all of my games on my right hand screen. Windowed borderless is so dark you can't find loot or anything in buildings unless it's daytime. Windowed mode and borderless need a gamma fix or something. Other than this .61 is running smooth for me and is just teasing me! I want to put more time into it to test things out but this monitor issue is keeping me away.