Haven't tracked this down further, but I have, with luck, two Windows
builds for 24.2.50.1 from 2012-08-26.  One of them has the problem, one
does not.
 
The one that does not have a problem was from Dani Moncayo:
 
In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-08-26 on DANI-PC
Bzr revision: 109787 cyd@gnu.org-20120826134218-63vsnbjvm5rcbzi7
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -I../../libs/libxpm-3.5.8/include -I../../libs/libxpm-3.5.8/src
 -I../../libs/libpng-1.4.10 -I../../libs/zlib-1.2.6
 -I../../libs/giflib-4.1.4-1/include -I../../libs/jpeg-6b-4/include
 -I../../libs/tiff-3.8.2-1/include
 -I../../libs/libxml2-2.7.8-w32-bin/include/libxml2
 -I../../libs/gnutls-3.0.16/include
 -I../../libs/libiconv-1.14-2-mingw32-dev/include'
 
The one that has the problem is the Emacs 24.2 release candidate, from
Christopher Scholtes:
 
  The Emacs 24.2 Release Candidate 2 Windows Binaries have been
  published in
  http://alpha.gnu.org/gnu/emacs/pretest/windows/
  The binaries were built using the following libraries:
  giflib-4.1.4-1
  gnutls-3.0.9
  jpeg-6b-4
  libXpm-3.5.8
  libpng-1.4.3-1
  tiff-3.8.2-1
  zlib-1.2.5-2

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-08-26 on MARVIN
Bzr revision: 109788 dmantipov@yandex.ru-20120827041533-3cy7pdjdqz14o90c
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'
 
The problem is shown in the two attachments.  Look at the line
 -- Function: insert-before-markers-and-inherit
It is not highlighted, but it should be.
 
And look at the line "Here are the functions that insert...".
It is highlighted, but it should not be.
 
The code that fontifies this is from info+.el, and it works correctly
with all Emacs versions.  ONLY the reference items (Variable, Function,
etc.), and EACH of the reference items, should be highlighted with the
light gray background.
 
This is the code, though I doubt it is relevant to the problem:
 
(defun info-fontify-reference-items ()
  "Fontify reference items such as \"Function:\" in Info buffer."
  (while (re-search-forward 
           "^ --? \\(Command:\\|Constant:\\|Function:\\|Macro:\\|\
Special Form:\\|Syntax class:\\|User Option:\\|\
Variable:\\)\\(.*\\)\\([\n]          \\(.*\\)\\)*"
           nil t)
    (let ((symb  (intern (match-string 1))))
      (put-text-property (match-beginning 1)
                         (match-end 1)
                         'font-lock-face
                         (case symb
                           ('Constant:       'info-constant-ref-item)
                           ('Command:        'info-command-ref-item)
                           ('Function:       'info-function-ref-item)
                           ('Macro:          'info-macro-ref-item)
                           ('Special\ Form:  'info-special-form-ref-item)
                           ('Syntax\ class:  'info-syntax-class-item)
                           ('User\ Option:   'info-user-option-ref-item)
                           ('Variable:       'info-variable-ref-item)))
      (put-text-property (match-beginning 2) (match-end 2)
                         'font-lock-face 'info-reference-item)
      (when (match-beginning 4)
        (put-text-property (match-beginning 4) (match-end 4)
                           'font-lock-face 'info-reference-item)))))