scrolling causes infinite elisp loop

[Craig Falls]

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In GNU Emacs 21.3.2 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-04-24 on raven, modified by Debian
configured using `configure  i386-linux --prefix=/usr --sharedstatedir=/var/lib 
--libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info 
--mandir=/usr/share/man --with-pop=yes --with-x=yes --with-x-toolkit=athena 
--without-gif'
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: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

REPRODUCING:

Run the follow elisp:
                (setq scroll-step                                               
          0)
                (setq scroll-margin             8)
                (setq scroll-conservatively     18)
                (setq next-screen-context-lines 18)

Then, scroll down past the end of the buffer quickly.  A good way to
                do this is by using the scroll wheel on your mouse.  I find that
                holding C-n or C-v rarely (if ever) generates the bug.  It 
appears
                to be a never-ending loop in the elisp not in the emacs 
executable
                itself.  C-g will not allow me to regain control, forcing me to
                use xkill or some such.

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

Recent messages:
Scanning buffer for index ( 40%)
Scanning buffer for index ( 48%)
Scanning buffer for index ( 59%)
Scanning buffer for index ( 98%)
Scanning buffer for index (100%)
Mark saved where search started
Mark set
Quit
keyboard-quit: Quit
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