> > Actually, I see that NEWS item, but I do not think I see
> > that behavior, IIUC.  In emacs -Q, for instance, if I do
> > `M-x customize-option auto-coding-alist', I
> > see the full standard (uncustomized) value immediately.  
> > (I'm using MS Windows, in case that makes a difference.)
>
> Thank you for looking into this.
>
> You are right, with M-x customize-option such behaviour does
> not happen.  Try customize-group, please.

So that NEWS item is partly incorrect, and misleading.  What is described does
not happen in general when customizing options, but only in a particular case.

You might want to report that (doc) bug also.

> > At any rate, if some Customize behavior does not seem right
> > to you, or if it does not seem understandable or correctly
> > documented, then consider filing a bug report or an enhancement
> > request.
>
> I'm going to.