bug#2435: 23.0.90; customize/whitespace: display stops updating

When scrolling down the Whitespace group in Customize, the display
stops updating, probably when reaching the Hspace Regexp entry
containing exotic characters with different character height. However,
Emacs is not frozen and just switching to another buffer and back to
customize is enough to work the issue around. After the switch,
Customize works normally, including the Hspace Regexp entry.

Steps to reproduce here:

M-x customize-group whitespace
press Page Down
Customize window now stops updating until I switch to another buffer
and back



In GNU Emacs 23.0.90.1 (x86_64-pc-linux-gnu, GTK+ Version 2.12.12)
 of 2009-02-22 on elegiac, modified by Debian
 (emacs-snapshot package, version 1:20090222-1)
Windowing system distributor `The X.Org Foundation', version 11.0.10402000
configured using `configure  '--build' 'x86_64-linux-gnu' '--host' 'x86_64-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.0.90/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.0.90/site-lisp:/usr/share/emacs/site-lisp' '--with-x=yes' '--with-x-toolkit=gtk' 'build_alias=x86_64-linux-gnu' 'host_alias=x86_64-linux-gnu' 'CFLAGS=-DDEBIAN -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed' 'CPPFLAGS=''

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_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Help

Minor modes in effect:
  show-paren-mode: t
  server-mode: t
  global-whitespace-newline-mode: t
  global-whitespace-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t
  view-mode: t

Recent input:
0 8 9 0 7 8 9 <down-mouse-1> <mouse-1> h f h d f g 
h d f g h C-c C-c M-x m a i l <return> <home> <return> 
<up> F r o m : SPC m a k o v i c k @ g m a i l . c 
o m <down> m a k o v i c k @ g m a i l . c o m <down> 
s d f a s d f a <down-mouse-1> <mouse-1> a s d f a 
s d f C-c C-c C-h C-g M-x c u s t <tab> - g <tab> m 
<backspace> <return> m a i l <return> <help-echo> <help-echo> 
<help-echo> <down-mouse-1> <help-echo> <down-mouse-1> 
<help-echo> <down-mouse-1> <down-mouse-5> <mouse-5> 
<down-mouse-5> <mouse-5> <down-mouse-5> <mouse-5> <help-echo> 
<down-mouse-1> <mouse-2> <help-echo> <down-mouse-1> 
<help-echo> <down-mouse-1> <mouse-1> <down-mouse-5> 
<mouse-5> <down-mouse-5> <mouse-5> <double-down-mouse-5> 
<double-mouse-5> <down-mouse-5> <mouse-5> <double-down-mouse-5> 
<double-mouse-5> <triple-down-mouse-5> <triple-mouse-5> 
<down-mouse-4> <mouse-4> <help-echo> M-x s e <backspace> 
m a <tab> ` 1 <backspace> <backspace> <tab> <backspace> 
<backspace> e n d m <tab> <tab> <tab> <backspace> <backspace> 
<backspace> <backspace> <backspace> m a i l <tab> <return> 
C-x k <return> <help-echo> <help-echo> <down-mouse-4> 
<mouse-4> <double-down-mouse-4> <double-mouse-4> <down-mouse-5> 
<mouse-5> <down-mouse-5> <mouse-5> <double-down-mouse-5> 
<double-mouse-5> <down-mouse-5> <mouse-5> <next> <prior> 
<help-echo> <help-echo> <help-echo> <help-echo> <down-mouse-1> 
<down-mouse-1> <down-mouse-1> <down-mouse-1> <mouse-1> 
<help-echo> <down-mouse-1> <help-echo> <down-mouse-4> 
<mouse-4> <double-down-mouse-4> <double-mouse-4> <triple-down-mouse-4> 
<triple-mouse-4> <down-mouse-5> <mouse-5> <down-mouse-4> 
<mouse-4> <double-down-mouse-4> <double-mouse-4> <down-mouse-4> 
<mouse-4> <double-down-mouse-4> <double-mouse-4> <triple-down-mouse-4> 
<triple-mouse-4> <triple-down-mouse-4> <triple-mouse-4> 
l l <down-mouse-1> <down-mouse-1> <mouse-1> <help-echo> 
<down-mouse-1> <help-echo> <down-mouse-1> <mouse-1> 
M-x <up> <return> m a k o v i c k @ g m a i l . c o 
m <down> v x z v z x c v <down-mouse-1> z x <drag-mouse-1> 
c v z x c C-c C-c M-x b u g <backspace> <backspace> 
<backspace> <backspace> <up> <up> <up> <up> <up> <down> 
<return>

Recent messages:
To install your edits, invoke [State] and choose the Set operation
Mark set
byte-code: Beginning of buffer [2 times]
Custom-no-edit: You can't edit this part of the Custom buffer [2 times]
To install your edits, invoke [State] and choose the Set operation
Saving file /home/henry/.emacs...
Wrote /home/henry/.emacs
Mark set
Sending...done
call-interactively: Text is read-only