Subject: bug#23129: 25.1.50; Prefix key is not echoed during minibuffer completion

From: Drew Adams <[email-masked]>
Date: Sun, 27 Mar 2016 15:34:02 -0700 (PDT)

0. emacs -Q

1. 
(defvar bar-map nil)
(define-prefix-command 'bar-map)
(define-key minibuffer-local-must-match-map "\M-i" 'bar-map)
(define-key bar-map "\M-z" 'foo)
(defun foo () (interactive) (message "FOOOOOOOOOOO") (sleep-for 2))

`M-x M-i'
Wait a second.  The prefix key `M-i' is NOT echoed.
`M-z'
The message from `foo' is shown.

2. 
(global-set-key "\M-l" 'bar-map)

`M-l'
Wait a second.  The prefix key `M-l' IS echoed.
`M-z'
The message from `foo' is shown.

BUG: The prefix key `M-i' should be echoed during completion.

In GNU Emacs 25.1.50.1 (i686-pc-mingw32)
 of 2015-12-10
Repository revision: 6148555ee5a3d0139ae517803718b3e0357933c7
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Configured using:
 'configure --prefix=/c/Devel/emacs/snapshot/trunk --enable-checking=yes
 --enable-check-lisp-object-type --without-compress-install 'CFLAGS=-Og
 -ggdb3' LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''