bug#38016: 27.0.50; Display issues with delay-warning and side-by-side windows in terminal

[Tom Levy <tomlevy93@gmail.com>]

Steps:
Maximize a terminal window to make Emacs use a side-by-side window split.
Run: emacs -Q -nw --eval '(delay-warning :debug "line 1\nline 2")'
The *scratch* and *Warnings* buffers should be displayed side by side.
Press M-< C-e RET DEL (in the *scratch* buffer).
Line 2 in the *Warnings* buffer disappears (!)

Variation: run Emacs as before, but press M-< C-e a RET
Line 2 in the *Warnings* buffer moves down (!)

Happens in master (27.0.50) and 24.5.1, with both gnome-terminal and
xterm.



In GNU Emacs 27.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-11-01 built on localhost
Repository revision: 9d209c90345df6c39310912ba04ca02473a24bed
Repository branch: master
System Description: Debian GNU/Linux 10 (buster)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD PDUMPER
LCMS2 GMP

Important settings:
  value of $LANG: en_US.UTF-8
  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
  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 dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader cl-loaddefs cl-lib sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils warnings term/xterm xterm
byte-opt gv bytecomp byte-compile cconv 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 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 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 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 lcms2 dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 48787 4146)
 (symbols 48 6105 1)
 (strings 32 15685 1644)
 (string-bytes 1 503280)
 (vectors 16 7236)
 (vector-slots 8 77463 6914)
 (floats 8 23 379)
 (intervals 56 182 0)
 (buffers 1000 12))