bug#5122: Mismatched parentheses when dealing with huge buffer content

In GNU Emacs 23.1.1 (i386-mingw-nt6.0.6002)
 of 2009-07-30 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 6.0.6002
configured using `configure --with-gcc (4.4)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  shell-dirtrack-mode: t
  rcirc-track-minor-mode: t
  diff-auto-refine-mode: t
  yas/global-mode: t
  yas/minor-mode: t
  global-auto-complete-mode: t
  auto-complete-mode: t
  cua-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
M-k C-n <C-return> M-f C-g C-g <C-return> C-f C-f C-f
C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f C-f
C-f C-f C-f C-f C-f C-f C-f C-f C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v C-v
C-v C-v C-v C-v C-v C-v C-v M-v M-v M-v M-v M-v M-v
M-v M-v M-v M-v C-v C-n C-n C-n C-n C-n C-n C-n C-n
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n
C-n C-n C-n C-n C-n C-n C-n M-k C-g M-< C-n C-p M-n
C-p C-e <backspace> ) C-t C-s M-< M-n M-v <down-mouse-1>
<mouse-movement> <down-mouse-4> <drag-mouse-1> C-t
o C-t C-g C-h v <up> <return> C-n C-n C-n C-t o C-n
C-n C-n C-n C-n C-n C-n C-SPC M-n M-w C-t o C-t u s
c r a <return> C-y M-< C-n C-n M-> C-p C-e <backspace>
) M-x r e p o r t - e m a c s <tab> <return>

When taking the value of ucs-completions given by C-h v
ucs-completions and inserting it in the scratch buffer, Emacs is
unable to determine that a correct parentheses match is made. (Pardon
my English.) I simply remove the last of the two trailing parentheses
of the expression and insert a new trailing parenthesis (making the
content identical to what it was initially), and I get "Mismatched
parentheses".

-- 
Deniz Dogan