Although I love the Navigation Ball, and use it frequently, thought I would see what happens if I turn it off and then reboot...
Yes, indeed, it turns itself back on. I experimented a couple of times, and it happened both times.
From what I could see, even if you go into the "Manage Apps" under "Settings", you don not have the option to disable it. You may want to go to the Onyx BBS site to raise this issue.
http://bbs.onyx-international.com/