To reproduce:
Enable the XKB "mouse keys" accessibility feature with
xmodmap -e 'keysym Num_Lock = Num_Lock Pointer_EnableKeys'
Then switch it on by pressing <Shift>-<NumLock> while numlock state is off.
Now you can use the number keys on the numeric keypad around the 5 to move the mouse pointer in the corresponding directions.

Problem:
The Nine doesn't move the pointer up+right, as would fit into the system, but it behaves like the Eight, moving straight upwards.

Fix:
The following patch helped on my Gentoo system.

--- xorg-server-1.3.0.0.orig/xkb/xkbDflts.h     2007-10-14 08:06:41.000000000 +0200
+++ xorg-server-1.3.0.0/xkb/xkbDflts.h  2007-10-14 08:08:10.000000000 +0200
@@ -281,7 +281,7 @@
     {    XK_KP_9, 0x0001,
          XkbSI_AnyOfOrNone, 0xff,
          255,
-       {        XkbSA_MovePtr, { 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00 } } },
+       {        XkbSA_MovePtr, { 0x00, 0x00, 0x01, 0xff, 0xff, 0x00, 0x00 } } },
     {    XK_KP_Prior, 0x0001,
          XkbSI_AnyOfOrNone, 0xff,
          255,