Heh. I actually did misunderstand. :-)
In the terminal window, shift-arrow-up and shift-arrow-down work. Shift-page-up works. Shift-page-down does not.
I ran the "xev |grep -B 2 -A 3 Next" test. Put the arrow in the white rectangle and pressed any number of keys, including page-down and got no output. Ran xev without the grep, and pressing page-down gave the following response (I think this is the right one):
KeyPress event, serial 39, synthetic NO, window 0x1200001,
root 0x101, subw 0x0, time 52412923, (1,20), root:(805,311),
state 0x0, keycode 105 (keysym 0xffe4, Control_R), same_screen YES,
XLookupString gives 0 bytes:
XmbLookupString gives 0 bytes:
XFilterEvent returns: False
Does that help?