bug#5030: 23.1.50; Unexpected minibuffer tab completion behavior

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the [email protected] mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug.  If you can, give
a recipe starting from `emacs -Q':

On my computer, I have only two files in my home directory beginning
with the letter 'a': ~/aaa and ~/aab.  After starting Emacs with "Emacs
-Q" and pressing "C-x C-k C-a C-k ~ / <tab> <tab>", a new window appears
to display the *Completion* buffer with all of the files in my home
directory.  I expect this.

After additionally pressing "a <tab>", the minibuffer completes to
"~/aa", and the window that previously displayed the *Completion* buffer
now switches to displaying the *Messages* buffer instead.  I don't
expect this.

Instead, I expect either for that window to continue showing the
*Completion* buffer (refreshed to display just the "aaa" and "aab"
entries) or for that window to be deleted.  (I'd prefer the former
behavior.)

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
/Volumes/Disk Image/emacs-build/obj/nextstep/Emacs.app/Contents/Resources/etc/DEBUG.


In GNU Emacs 23.1.50.1 (i386-apple-darwin9.8.0, NS apple-appkit-949.54)
 of 2009-11-23 on admins-macbook-pro-2.local
Windowing system distributor `Apple', version 10.3.949
configured using `configure  '--with-ns' '--without-x''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x C-f C-a C-k ~ / <tab> <tab> a <tab> C-g M-x r e
p o r t - e m a c s - b u g <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
Quit

Load-path shadows:
None found.

Features:
(shadow mail-extr message ecomplete rfc822 mml mml-sec password-cache
mm-decode mm-bodies mm-encode mailcap mail-parse rfc2231 rfc2047 rfc2045
qp ietf-drums mailabbrev nnheader gnus-util netrc time-date mm-util
mail-prsvr gmm-utils wid-edit mailheader canlock sha1 hex-util hashcash
mail-utils emacsbug sendmail regexp-opt help-mode view tooltip
ediff-hook vc-hooks lisp-float-type mwheel ns-win easymenu tool-bar dnd
fontset image fringe lisp-mode register page menu-bar rfn-eshadow timer
select scroll-bar mldrag mouse jit-lock font-lock syntax facemenu
font-core frame cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev loaddefs button minibuffer faces
cus-face text-properties overlay md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process ns
multi-tty emacs)