I have the same problem. I only have Options button and I also set NEI enabled(both World and Global).
And my OS is WIN7, My JAVA's version is 1.8.0_25
I try to press O but it just hide/show the Options button.
This is my config http://pastebin.com/EfTfjAPw
There is a way to fix it. Game menu→Options→Video Settings→GUI scale: Large(DO NOT use AUTO!!)