bug#23594: 25.0.94; Display errors on Linux tty

[Alan Mackenzie <acm@muc.de>]

In GNU Emacs 25.0.94.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.7)
 of 2016-05-17 built on acm
Configured using:
 'configure --with-tiff=no --with-gif=no --with-gpm'

Configured features:
XPM JPEG PNG RSVG SOUND GPM DBUS GSETTINGS NOTIFY ACL GNUTLS LIBXML2
FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

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

Major mode: C/l

Minor modes in effect:
  gpm-mouse-mode: t
  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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

(This is the latest pretest version.)

emacs -Q
C-x b foo.c
M-x c-mode

Type the following five lines into the buffer:
#########################################################################
char foo [] = "foo";

#define FOO BAR

char bar [] = "bar";
#########################################################################

Move point to just after "BAR" on line 3.
C-u C-x =

There are now two display bugs evident:
1. The vertical divider between the two windows is missing a piece just
after the line "  decomposition: (10) ('" in *Help*.

2. In foo.c, the actual text display is out of sync with the text cursor.
The text has been scrolled one line up, but the cursor has remained at
the same position in the window, apparently at the end of a non-existent
line of spaces.  The cursor can be freely moved, but is one line out of
sync with the displayed text.

Type C-l one or more times.  The foo.c window becomes increasingly
confused.  Type <backspace>.  This causes even more confusion.

The bugs are not evident in X-Windows.

-- 
Alan Mackenzie (Nuremberg, Germany).