Error displaying a frame modified with (tool-bar-lines . 0)

[Juanma Barranquero]

After much back and forth, bug#17046 has been determined to be that running

  emacs -Q -l bug.el

with bug.el:

;;; bug.el
(let* ((default-frame-alist nil)
       (frame (make-frame '((width . 80) (height . 20))))
       (lines (frame-parameter frame 'tool-bar-lines)))
  (discard-input)
  (read-event nil nil 2)
  (modify-frame-parameters frame '((tool-bar-lines . 0)
                                   (width . 60) (height . 25)))
  (modify-frame-parameters frame `((tool-bar-lines . ,lines))))
;;, end

causes the frame to be redisplayed incorrectly (the trigger being the
(tool-bar-lines .0) parameter:

http://debbugs.gnu.org/cgi/bugreport.cgi?msg=26;filename=emacs-sshot.png;att=1;bug=17046

This happens on a Ubuntu 13.10:

GNU Emacs 24.3.50.2 (i686-pc-linux-gnu, GTK+ Version 3.8.6)
 of 2014-03-14 on poulenc
Repository revision: 116756 rudalics <at> gmx.at-20140314103846-ytcz7b30ocmzo8jh
Windowing system distributor `The X.Org Foundation', version 11.0.11405000
System Description: Ubuntu 13.10

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

Anyone knowledgeable about this kind of issue is welcome to drop by bug#17046.

TIA,

   J