Reassigning AE-L/AF-AF-L button to AF-ON

I need your help understanding something.

I reassigned AE-L/AF-L button to AF-ON according to the info on page 256 of the manual (see below).

It's my understanding that you use AF-ON to focus, release the button to lock focus (even in AFC), and then re-compose. The problem is once I use AF-ON to lock focus and press shutter release button to capture the image, it re-focuses to the AF focus point of the re-composed view.

Note: In the past, I've moved my AF focus point avoiding the need to lock focus and re-compose but I don't want to do that right now.

So here's my setup:

IN-CAMERA
Aperture priority mode
AF ON
AFC + S

LENS
18-200MM
M/AF
VR ON + NORMAL

Cheers

When I set my AE-L/AF-L to AF ON, the shutter does not refocus...