bug#37784: Buffer messed up when scrolling undecorated frame

[Carlos Pita]

When I set:

(set-frame-parameter nil 'undecorated t)

and then change to another window and back to emacs, then scroll
around the window, I often end up with a very messed up buffer and
have to run redraw-display in order to sanitize its contents. See
attached screenshot.

I've tested this in an environment featuring:

* Gnome 3.32
* Ubuntu 19.04
* Emacs built from emacs-26 branch (of course, run with -Q)

After restoring decorations the problem stop happening.

Any idea about what could be causing this?

Best regards
--
Carlos

---

In GNU Emacs 26.3.50 (build 11, x86_64-pc-linux-gnu, GTK+ Version
3.24.8, cairo version 1.16.0)
 of 2019-10-16 built on carlos
Repository revision: 116a7369bcb97341be7d6ffe3f832bf52159a99a
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Ubuntu 19.04

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured using:
 'configure --prefix=/home/carlos/Local/stow/emacs-26 --with-cairo
 'CFLAGS=-O3 -g0''

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY LIBSELINUX
GNUTLS FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS

Important settings:
  value of $LC_MONETARY: es_AR.UTF-8
  value of $LC_NUMERIC: es_AR.UTF-8
  value of $LC_TIME: es_AR.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors 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 composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray 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 threads dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 94873 8334)
 (symbols 48 20247 1)
 (miscs 40 44 118)
 (strings 32 28311 1604)
 (string-bytes 1 753138)
 (vectors 16 13910)
 (vector-slots 8 501264 11006)
 (floats 8 49 68)
 (intervals 56 231 0)
 (buffers 992 12))

Screenshot from 2019-10-16 21-38-59.png
Description: PNG image