I doubt this is the issue causing the problem, but I'll give my input anyway.
Last week I installed a new live wallpaper called "3d effect" live wallpaper. I used it for 1 day, then my capacitive buttons started going haywire. Even a battrey pull would not fix the issue.
So, I uninstalled this wallpaper & the buttons worked again.
It was probably just a coincidence that the wallpaper uninstall "seemingly" fixed the issue for me, but who knows.
I am in no way knocking the wallpaper, but am just putting my two cents in just in case anyone else reading this thread has the same circumstances as I did.
Sent from my Nexus S 4G using TapaTalk. Kay pof shinum wif a bardle doo.