Hey all, I've been having this issue with fullscreen applications where they all want to span across 3 monitors. It becomes a major problem for certain games where I can't actually see the resolution options because they are off my monitors.
My monitors are not horizontally alligned, but I only recently developed this issue, most games were able to stick to just my main monitor
Attached is what happens when I open the game The Binding of Isaac. Even though it is set to full screen, you can see my steam peaking through behind it, and how it spans across all my monitors. Any ideas for a fix?

Yeah, still happens, even after a restart with DF turned off. Here's the attachment

Try installing and using 9.9, that worked for me.