bug#2957: 23.0.92; ucs-insert: Completion does not work correctly with Unicode Character Name Input

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:

BUG DESCRIPTION:
When I type the following:
C-x 8 RET greek letter alpha
and press TAB, I get several choices for the greek letter alpha
variants. But I'm unable to type anything into the minibuffer (neither
SPC nor any character) -- Emacs just doesn't accept the input. If I
press RET at this point, I get the error message "ucs-insert: Not a
Unicode character code: nil".
I tried with "emacs -Q" (no init files), and I still get this
incorrect 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'.
If you would like to further debug the crash, please read the file
d:/Progs/emacs/etc/DEBUG for instructions.


In GNU Emacs 23.0.92.1 (i386-mingw-nt5.1.2600)
 of 2009-03-31 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'

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: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-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:
M-x C-g C-x 8 <return> g r e e k SPC l e <tab> <tab>
a l p <tab> <tab> SPC SPC SPC w <tab> <tab> <backspace>
<tab> <tab> <return> M-x r e p o r t - e m <tab> <
return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
Loading Unicode character names...done
Making completion list... [6 times]
ucs-insert: Not a Unicode character code: nil