bug#27014: 26.0.50; auto-hscroll-mode and tabulated-list-mode

[Stephen Berman]

0. emacs -Q
1. Set auto-hscroll-mode to `current-line'.
2. Visit a buffer that uses tabulated-list-mode, e.g. Buffer Menu (C-x
   C-b), Package Menu (M-x list-packages), Proced (M-x proced), making
   sure that the buffer contains at least one truncated line and a line
   below it.
3. Advance point along the truncated line (e.g. by repeating C-f or M-f
   or with C-e).
=> When point gets within hscroll-margin columns of the right window
   edge (or further), instead of the current line being scrolled, the
   one below it is.

(In addition, with Proced, the header line is also scrolled, but that
seems to be a Proced bug, since that also happens when auto-hscroll-mode
is set to t; and with Buffer Menu or Package Menu the header line does
not scroll with either setting of auto-hscroll-mode.)

In GNU Emacs 26.0.50 (build 14, x86_64-pc-linux-gnu, GTK+ Version 3.22.8)
 of 2017-05-21 built on rosalinde
Repository revision: 08212929ba7052883bd506be320dfaaae5b68970
Windowing system distributor 'The X.Org Foundation', version 11.0.11901000

Configured using:
 'configure 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

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