I don't know anything about the software version for the 770, but the "gtk-scrolled-window-placement" setting was implemented in GTK2 version 2.10

I would be willing to state that the 770 OS you are using has an older version of GTK2 than that. There is a chance that if you upgrade to a newer hacker-edition it will bring the package up to an acceptable level, but I can't guarantee that.