Overlay with before-string prevents vertical motion

[Ralf Angeli]

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

If you execute the code snippet

(progn
  (insert "\nfoo\n")
  (let ((ov (make-overlay (- (point) 4) (point))))
    (overlay-put ov 'before-string "x\n")))

in the *scratch* buffer and try to move point upwards with `C-p', you
can see that it is not possible to move past the "x" which is part of
the overlay's before-string property.  This affects e.g. preview-latex
where it is currently impossible to move point upwards out of opened
previews with `C-p'.


In GNU Emacs 21.3.50.1 (i686-pc-linux-gnu, GTK+ Version 2.4.14)
 of 2005-01-22 on neutrino
Distributor `The XFree86 Project, Inc', version 11.0.40300001
configured using `configure '--with-gtk''

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
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  display-time-mode: t
  iswitchb-mode: t
  show-paren-mode: t
  encoded-kbd-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<down> <down> <down> M-w <return> <return> <return> 
C-y <up> <up> <up> <right> C-SPC C-g <down> <return> 
<up> <tab> ( g o t o - c h a r SPC ( - SPC ( p o i 
n t ) SPC 4 ) ) ) C-x C-e C-_ C-_ C-_ C-_ C-_ C-_ C-_ 
C-_ <down> <down> <return> <left> C-x C-e <up> <up> 
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up> 
<up> <up> <down> <down> <up> <up> <up> <up> <up> <up> 
<up> <up> <up> M-x r e p o t <backspace> r t - e m 
<tab> <return>

Recent messages:
Mark set
call-interactively: Beginning of buffer [2 times]
Undo!
Mark set [3 times]
Quit
183
Undo! [8 times]
"x
"
Loading emacsbug...done