When:

- 2 windows open the same file
- There's a timer dealing with modeline or header-line format

Then pressing `C-g` sometimes scrolls the buffer in this window to the
position in the other window.

Here's a recipe for reproduce:

- `$ emacs -Q`

- Eval this:
  ```
  (run-with-timer 0 0.1 (lambda () (setq mode-line-format "hi")))
  ```

- `M-x delete-other-windows` so we have only one window.

- `C-x C-f` to open a file. I use
  <https://github.com/lsof-org/lsof/blob/master/main.c> when testing,
  but any file that's long enough should work.

- `M-x split-window-horizontally`, so we have 2 windows viewing the same
  file. For some reason, splitting vertically doesn't trigger the
  problem.

- Scroll one window down to somethere.

- Hold `C-g` or press it repeatedly and quickly, then the window will go
  to the same position in file as the other window.

You can do the same with `header-line-format`, it also has the problem.
Using `run-with-idle-timer` instead seems doesn't have the problem.

See also <https://github.com/kiennq/emacs-mini-modeline/issues/45> where
I report the same problem. I believe another package that's influenced
by this is <https://github.com/purcell/mode-line-bell>.

--- Info generated by `report-emacs-bug` ---

In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, cairo version 1.17.3)
 of 2020-08-29 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
System Description: Manjaro Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set
[nil 24482 55348 93490 0.1 (closure (t) nil (setq mode-line-format "hi")) nil nil 920000]
You can run the command ‘split-window-horizontally’ with M-x sp-h RET
Quit [22 times]
Quit
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
 --with-modules --with-cairo --with-harfbuzz 'CFLAGS=-march=x86-64
 -mtune=generic -O2 -pipe -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
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INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
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PDUMPER LCMS2 GMP

Important settings:
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  value of $LC_NUMERIC: zh_CN.UTF-8
  value of $LC_TIME: zh_CN.UTF-8
  value of $LANG: zh_CN.utf8
  value of $XMODIFIERS: @im=fcitx
  locale-coding-system: utf-8-unix

Major mode: C/*l

Minor modes in effect:
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  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
  abbrev-mode: t

Load-path shadows:
None found.

Features:
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regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic cham georgian
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Memory information:
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 (symbols 48 8992 1)
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 (string-bytes 1 858985)
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 (vector-slots 8 224399 9036)
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