I have Sleep When Inactive For: DO Not Suspend. While Plugged in set. And Turn Screen Off When Inactive For: Never. Set.
Also accessing these options appears in two different settings screens. There is a different settings screen when I access this from the wing panel than when I access it from the "settings" icon. I have seen other people mention that they have two settings windows also. As far as I remember I did not install the separate "Gnome-Settings" on my own, but I could be wrong.