Mouse keys don't move cursor

I have set up a 3Dconnexions spacemouse to among other things, drive the cursor around using axis movements. This works in Finder, when I set Universal Access for Mouse Keys On. I can drive the cursor left and right with the U and O keys. (It is a PowerBook.) However, when I switch to TextEdit, the spacemouse input just types a bunch of U's and O's instead of moving the cursor. When I use the keyboard to press U or O, the cursor moves as expected.

How can I get my axis inputs to move the cursor?

OS X 10.8.