bug#5177: 23.1.90; scrollbar thumb stops working after being dragged

[Ken Brown <kbrown@cornell.edu>]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org mailing 
list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug.  If you can, give
a recipe starting from `emacs -Q':

1. Start the Gtk+ build of emacs.
2. Visit a file too big to fit in the window.
3. Drag the (vertical) scrollbar thumb.
4. Scroll through the buffer using the mouse wheel or keystrokes.

The scrollbar thumb stays fixed and no longer shows the relative
position in the buffer.  Clicking in an empty area of the scrollbar
restores the correct behavior.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
     `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/usr/share/emacs/23.1.90/etc/DEBUG.


In GNU Emacs 23.1.90.1 (i686-pc-cygwin, GTK+ Version 2.18.3)
  of 2009-12-10 on markov
Windowing system distributor `The Cygwin/X Project', version 11.0.10701000
configured using `configure 
'--srcdir=/usr/src/emacs-23.1.90-1/src/emacs-23.1.90' '--prefix=/usr' 
'--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' 
'--libexecdir=/usr/lib' '--datadir=/usr/share' '--localstatedir=/var' 
'--sysconfdir=/etc' '--datarootdir=/usr/share' 
'--docdir=/usr/share/doc/emacs' 'CC=gcc' 'CFLAGS=-O2 -pipe ' 'LDFLAGS=' 
'LIBS=' '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: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   mouse-wheel-mode: t
   tool-bar-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
   line-number-mode: t
   transient-mark-mode: t

Recent input:
<help-echo> <help-echo> M-x r e p o r t - e m <tab>
<return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow mail-extr message ecomplete rfc822 mml easymenu mml-sec
password-cache mm-decode mm-bodies mm-encode mailcap mail-parse rfc2231
rfc2047 rfc2045 qp ietf-drums mailabbrev nnheader gnus-util netrc
time-date mm-util mail-prsvr gmm-utils wid-edit mailheader canlock sha1
hex-util hashcash mail-utils warnings emacsbug sendmail regexp-opt
tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd
font-setting tool-bar dnd fontset image fringe lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mldrag mouse jit-lock
font-lock syntax facemenu font-core frame cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese hebrew
greek romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev loaddefs button
minibuffer faces cus-face text-properties overlay md5 base64 format env
code-pages mule custom widget hashtable-print-readable backquote
make-network-process font-render-setting gtk x-toolkit x multi-tty
emacs)