bug#7087: 24.0.50; cannot customize default-frame-alist - it says value is nil but it is not

[Drew Adams]

This is not starting from emacs -Q, but the setup is too long to
describe here.
 
In Emacs 23.2 and previous releases, there is no problem.
 
In this Emacs 24 build, M-x customize-option default-frame-alist gives a
Customize buffer that shows the value of the option as nil and says
"this option has been changed outside the customize buffer. (mismatch)".
However, C-h v default-frame-alist shows it has a non-nil value:
 
((foreground-color . "Black")
 (background-color . "LightBlue")
 (font . "-*-Lucida Console-normal-r-*-*-14-112-96-96-c-*-iso8859-1")
 (mouse-color . "Red")
 (cursor-color . "Red")
 (cursor-type . bar)
 (menu-bar-lines . 1)
 (top . 0)
 (left . 0)
 (width . 80)
 (height . 35)
 (minibuffer)
 (user-position . t)
 (vertical-scroll-bars . right)
 (icon-type)
 nil
 (left-fringe . 0)
 (right-fringe . 0)
 (fringe . 0))
 
Clearly there is a mismatch, not between the value and what the option
spec should be, but between what Customize thinks the value is and what
the value is in fact.  And even if the option value were nil, I don't
think that would signify a mismatch.  Something is very wrong here.
 

In GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600)
 of 2010-09-20 on 3249CTO
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.4) --no-opt --cflags
-Ic:/imagesupport/include'