I figured out the reason for the wrong text in the full screen keyboard. It's because you have to bind a function to the GtkIMContext retrieve-surrounding signal and call set_surrounding() from there with the content of the textarea. I have this halfway working, except that webkit crashes when the content of the full screen keyboard is committed...

But something else: Do you even bring up the full screen osk for HTML forms in bundyo's libwebkit? I couldn't get the full screen osk at all with the d-pad center button until i figured out how to trigger that (calling gtk_im_context_filter_keypress() in the key release function).