bug#14738: 24.3.50; defcustom :type (repeat (cons symbol plist)) when nil is the default value.

[Drew Adams]

> 0. C-M-x the below defcustom.  This is copied verbatim from gnus-art.el
> 1. M-x customize-variable RET gnus-face-properties-alist RET
> 2. The first PROP VALUE pair in the widget is more indented than the rest.
> 
> 3. Change the standard value to nil.  C-M-x it.
> 4. Note that the INS DEL button for the plist is not available.  i.e., I
>    cannot add more than one PROP VALUE pair.

FWIW, I do not see that behavior with emacs -Q in this build:

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-06-27 on ODIEONE
Bzr revision: 113205 dgutov@yandex.ru-20130627095155-f1lv1c7xf99g1sss
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 CFLAGS=-O0 -g3 LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

It behaves normally, AFAICT.  With nil as the default value,
I get a INS button, and after clicking it I get another one
(at the same level), so I can define any number of PROP VALUE pairs.

HTH.