Hello.

Recipe to reproduce this bug, starting from emacs -Q:
1) C-x b test
2) M-x text-mode
3) Type something like this:
One sentence.
Other sentence.

4) Go to the first sentence, after the period.  Type anything and then
type C-M-i to complete it.
I type "comple" and complete it to "complete".

5) I expect the cursor to be at the end of the word just completed.  But
I see it moving to the next line.  With different words completed, the
exact position changes, but to me the cursor always ends up in an
unexpected position.

Best regards,
Mauro.


In GNU Emacs 27.0.50 (build 51, i686-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2019-09-29 built on the-blackbeard
Repository revision: 46eb6df45358f413847ceb882898b2326f7584c8
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.
(New file)
Starting "look" process...

Configured using:
 'configure --enable-check-lisp-object-type'

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 THREADS PDUMPER LCMS2 GMP

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

Major mode: Text

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

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 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
ispell 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 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 48799 6392)
 (symbols 24 6117 1)
 (strings 16 16510 1760)
 (string-bytes 1 541197)
 (vectors 8 10909)
 (vector-slots 4 137958 17442)
 (floats 8 19 42)
 (intervals 28 194 7)
 (buffers 564 12)
 (heap 1024 7419 858))