bug#26852: 25.2; C-n may not keep column

[ynyaaa]

Evaluate the form below and resize frame
to hide the lower half of the window bottom line.
(hide digits and show the upper half of "X")

Then input C-n repeatedly to move down.
Each time the buffer is scrolled up,
the column of the cursor position moves right.

(let ((buf (generate-new-buffer "*tmp*"))
      (line (concat (propertize "X" 'face '(:height 5.0))
                    "01234567890123456789\n")))
  (switch-to-buffer buf)
  (dotimes (i 100)
    (insert (format "%2d " i) line))
  (goto-char (point-min))
  (forward-char 4))




In GNU Emacs 25.2.1 (i686-w64-mingw32)
 of 2017-04-25 built on LAPHROAIG
Windowing system distributor 'Microsoft Corp.', version 6.0.6002
Configured using:
 'configure --host=i686-w64-mingw32 --without-dbus
 --without-compress-install 'CFLAGS=-static -O2 -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-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 messages:

Load-path shadows:
None found.

Features:
(network-stream nsm starttls tls gnutls mailalias smtpmail auth-source
cl-seq eieio byte-opt bytecomp byte-compile cl-extra cconv eieio-core
cl-macs gv misearch multi-isearch pp shadow sort mail-extr emacsbug
message dired format-spec rfc822 mml mml-sec password-cache epg
epg-config gnus-util mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns help-mode easymenu cl-loaddefs pcase cl-lib mail-prsvr
mail-utils time-date mule-util japan-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp
disp-table w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded 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 w32notify w32 multi-tty
make-network-process emacs)

Memory information:
((conses 8 105635 16074)
 (symbols 32 21076 1)
 (miscs 32 93 212)
 (strings 16 20029 4289)
 (string-bytes 1 568121)
 (vectors 8 15089)
 (vector-slots 4 540256 8340)
 (floats 8 198 422)
 (intervals 28 456 32)
 (buffers 520 24))