bug#28622: 25.1; EasyPG conflicts with tar-mode

[address@hidden]

I start from 'emacs -Q' and I create an empty, encrypted tar file,
insert a file into it, and save it like so:

C-x C-f n e w . t a r . g p g <RET> I h e l l o . t x t <RET> C-x
C-s C-s O K <RET> <RET>

At this point, I enter a symmetric key from an external popup dialog:

t h i n g <RET> t h i n g <RET>

I then continue in emacs:

q C-x k <RET>

I open the encrypted tar file like so:

C-x C-f n e w . t a r . g p g <RET>

GPG Agent decrypts the file. What I expect to find is a buffer in
tar-mode, but I instead find a buffer in Fundamental mode with the
following message:

File mode specification error: (error Malformed Tar header)

Instead of a tar file encrypted with GPG, I instead have an encrypted
ASCII file with the same text as what was in the tar-mode buffer.



In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
of 2017-09-19, modified by Debian built on lgw01-amd64-019
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description: Ubuntu 17.04

Configured using:
'configure --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp

--with-sound=alsa --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp

--with-sound=alsa --with-x=yes --with-x-toolkit=gtk3
--with-toolkit-scroll-bars 'CFLAGS=-g -O2
-fdebug-prefix-map=/build/emacs25-i5Rf44/emacs25-25.1+1=.
-fstack-protector-strong
-Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
-D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX 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

Major mode: Fundamental

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

Recent messages:
Checking 57 files in /usr/share/emacs/25.1/lisp/calendar...
Checking 87 files in /usr/share/emacs/25.1/lisp/calc...
Checking 120 files in /usr/share/emacs/25.1/lisp/obsolete...
Checking for load-path shadows...done
You can run the command ‘report-emacs-bug’ with M-x r-em RET
Checking for load-path shadows...done
Undo!
mwheel-scroll: Beginning of buffer [6 times]
mwheel-scroll: End of buffer [4 times]
next-line: End of buffer
previous-line: Beginning of buffer

Load-path shadows:
None found.

Features:
(pp shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache gnus-util mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils misearch multi-isearch
apropos thingatpt help-fns help-mode easymenu wid-edit cl-loaddefs pcase
cl-lib epa-file epa derived epg epg-config jka-compr tar-mode time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core 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 charscript case-table epa-hook
jka-cmpr-hook help simple abbrev 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 dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 97865 13559)
(symbols 48 20624 1)
(miscs 40 71 279)
(strings 32 16766 4531)
(string-bytes 1 473696)
(vectors 16 13410)
(vector-slots 8 446423 9809)
(floats 8 175 104)
(intervals 56 773 0)
(buffers 976 27))