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.)
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. You can do either of those things using `M-x
report-emacs-bug'.