Kaushal Modi <kaushal.modi@gmail.com> writes:

> Have you looked at org-use-property-inheritance variable
> http://orgmode.org/manual/Property-inheritance.html -- You can set that to
> a regexp that does not match UNNUMBERED.

As this page mentions, default value is nil, which means nothing would be
inherited. UNNUMBERED does not follow this rule, even though it is not
mentioned as one “for which inheritance is hard-coded” in the manual ---
as was announced in org-news,
> *** Export unnumbered headlines

> Headlines, for which the property ~UNNUMBERED~ is non-nil, are now
> exported without section numbers irrespective of their levels.  The
> property is inherited by children.
http://orgmode.org/cgit.cgi/org-mode.git/plain/etc/ORG-NEWS

See also
Org Manual > Exporting > Export Settings
which also mentions
> Set `UNNUMBERED' property to non-`nil' to disable
>      numbering of heading and subheadings entirely.
Not a single word in the manual, or in worg, on disabling this
particular kind of inheritance.

After evaluating
(setq org-use-property-inheritance "[^\\(UNNUMBERED\\)]")
children are still exported numbered. org-reload has no additional
effect. I use Org 9.1.3 (20171116 from melpa) and Emacs 25.3.1.

In case UNNUMBERED's inheritance could be turned off by a standard
procedure, my other points are meaningless. So let's first figure out if
it could.