1D3 - keep losing access to ring of fire

I bought my 1D3 brand new last December - yellow dot, firmware 1.2.3, manufactured last September. Mostly everything about the camera is wonderful but I keep suffering one frustrating quirk and I don't understand where I'm going wrong.

I have been practicing action shots with my black dog running towards me. As there isn't much for the AF to pick up on, other than his teeth and tongue, I have been using mostly centre point with expansion points enabled all around. That all seems to work fine, much as I would expect.

However, I have also been trying ring of fire to see how the camera does in that mode. The problem is that I keep losing access to ring of fire. As far as I know I have my custom functions set up correctly, using the joystick only to select my AF point and with the dials disabled for AF selection. I have disabled the function that remembers a registered AF point and quick switches to that when I depress the joystick.

What I expect to happen is that I have centre point only selected and when I press the joystick it switches to ROF. When I press it again I switch back to the centre point. This works great, for a while, and then later on when I try to get ROF again I end up with some other single point instead and repeated pressing of the joystick just toggles back and forth between centre point and the other one, not centre point and ROF. I do not understand how or why I lose ROF.

It usually takes me a few minutes of random fumbling before I am able to get back to ROF again. Usually it seems that I have to re-enable the dials and twiddle them until ROF appears again. Once I have ROF back I can disable the dials and carry on as normal - until ROF vanishes again.

Is this a common problem? Am I just a klutz? Is there a quick way to get ROF back when it vanishes, without trawling through my custom functions?

Ok so as far as I know the joystick depression switches between a preregistered point and whatever point you were previously using. It sounds like you managed to register the center point, and then at some point switched to another point. You should register the ring of fire to the joystick in that case. I forget how to do it, it requires pressing a few buttons, but it's in the manual.

I could of course be completely wrong, this camera is so complex.

I believe you press and hold the AF Section button and then also press the ISO button at the same time to register the point - Intuitive! (not)

I'll give that a go. It just seems a mystery that it works OK for a while (well, as I would like it to) and then goes tits up at some point later on. It's not as though I have made any effort to keep changing the registered point, at least not intentionally .

EDIT : Done. Let's hope it stays put. Thanks for your help.