bug#17491: 24.3.90; overlay error in ediff

[Christopher Grubert]

I'm seeing broken behavior when running ediff-buffers on any buffers 
that cause at least one line to be highlighted in each buffer. As a 
trivial example I have two files, ~/a which contains the following two 
lines:
1
2

and ~/b which contains the following two lines:
3
4

Steps to reproduce:

emacs -Q
C-x C-f ~/a <RET>
C-x C-f ~/b <RET>
M-x ediff-buffers <RET>
a <RET>
b <RET>
n

It displays the both buffers and highlights both lines in each, but when 
pressing "n" to jump to next difference it fails to do so and this is 
displayed in the minibuffer:

Wrong type argument: listp, [#<overlay from 1 to 4 in a>]

System info follows:

In GNU Emacs 24.3.90.1 (x86_64-unknown-linux-gnu)
of 2014-04-16 on indigo
Windowing system distributor `Fedora Project', version 11.0.11404000
System Description: Fedora release 20 (Heisenbug)

Configured using:
`configure --prefix=/home/cgrubert/emacs-24.3.90 
--without-toolkit-scroll-bars --with-x-toolkit=no --with-imagemagick'

Important settings:
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: @im=none
locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
tooltip-mode: t
electric-indent-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
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t

Recent input:
C-x C-f a <return> C-x C-f b <return> M-x e d i f f
- b u f f e r s <return> a <return> b <return> n q
y <help-echo> M-x r e p o r t - e m a c s - b u g
<return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Computing differences between a and b ...
Buffer A: Processing difference region 0 of 1
Buffer B: Processing difference region 0 of 1
Processing difference regions ... done
Refining difference region 1 ...
ediff-set-fine-diff-properties: Wrong type argument: listp, [#<overlay 
from 1 to 4 in a>]
Quit this Ediff session? (y or n) y

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns mail-prsvr mail-utils ediff-merg ediff-wind ediff-diff
ediff-mult ediff-help ediff-init ediff-util ediff time-date tooltip
electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
lisp-mode prog-mode register page menu-bar rfn-eshadow timer select
scroll-bar 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 minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting x multi-tty emacs)

Memory information:
((conses 16 79887 5926)
(symbols 48 18808 0)
(miscs 40 62 149)
(strings 32 12140 4166)
(string-bytes 1 380185)
(vectors 16 9877)
(vector-slots 8 375656 5264)
(floats 8 79 166)
(intervals 56 219 14)
(buffers 960 16)
(heap 1024 36563 870))