Hello.

With current master:
1. emacs -Q
2. C-h i m Emacs RET
3. Type SPC.  I see some garbage text on the buffer.
For example, I can see part of the title "The Emacs Editor", and it stays
if I keep
typing SPC.

I have only managed to reproduce this in Info buffers.

Best regards,
Mauro.

In GNU Emacs 28.0.50 (build 2, i686-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2020-01-04 built on the-blackbeard
Repository revision: fb38d367f4a46c580510f8a6510ae8fb5f39222f
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 16.04.6 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
Composing main Info directory...done
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 PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: en_US.utf8
  value of $XMODIFIERS:
  locale-coding-system: utf-8-unix

Major mode: Info

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
  buffer-read-only: 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 mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs text-property-search time-date subr-x seq
byte-opt gv bytecomp byte-compile cconv 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
mule-util info easymenu 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 8 68892 5998)
 (symbols 24 6312 1)
 (strings 16 20629 2429)
 (string-bytes 1 631451)
 (vectors 8 10631)
 (vector-slots 4 139441 9274)
 (floats 8 22 23)
 (intervals 28 3522 0)
 (buffers 568 12)
 (heap 1024 9028 909))