mode-line redisplay bug

[Edward O'Connor]

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Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Every so often for a while I've occasionally seen this odd redisplay
bug, and I now think I know about it to report it. Anyway, here's what
happens: I set `mode-line-format' to nil in my eshell buffers. I switch
to an ERC buffer with the command `erc-track-switch-buffer' (which is
just a cute wrapper around `switch-to-buffer'). My mode-line in the ERC
buffer upon such a buffer switch will often be garbled, with only part
of it appearing, as you can see in this screenshot:

              http://edward.oconnor.cx/tmp/emacs/bug1.png

I thought that the bug might have something to do with my custom
`mode-line' face, but as you can see in this other screenshot, it occurs
with default Emacs faces as well:

              http://edward.oconnor.cx/tmp/emacs/bug2.png

(For completeness sake, here's what a normal ERC buffer looks like:
             http://edward.oconnor.cx/tmp/emacs/normal.png)

I imagine the redisplay code is trying to only redraw those parts of the
mode-line that have changed, or something like that. Nevertheless, it
does seem that the redisplay engine doesn't realize that, when switching
from a buffer without a mode-line, *everything in the mode-line* needs
to be redisplayed.

In GNU Emacs 22.0.50.1 (powerpc-apple-darwin8.1.0)
 of 2005-05-18 on roisin.local
Distributor `Apple Computers', version 10.4.1
configured using `configure '--enable-carbon-app' '--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: nil
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Major mode: Summary

Minor modes in effect:
  erc-truncate-mode: t
  erc-page-mode: t
  erc-services-mode: t
  erc-autojoin-mode: t
  erc-button-mode: t
  erc-ring-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  encoded-kbd-mode: t
  iswitchb-mode: t
  auto-insert-mode: t
  show-paren-mode: t
  minibuffer-electric-default-mode: t
  mouse-wheel-mode: t
  tooltip-mode: t
  auto-compression-mode: t
  menu-bar-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  temp-buffer-resize-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t
  next-error-follow-minor-mode:  Fol
  abbrev-mode: t

Recent input:
# e m a c s <return> <help-echo> s a e <backspace> 
y SPC c h e e s e C-a C-k s-z s-z s-z s-z s-z s-z <help-echo> 
M-x g n u s <return> <return> <return> SPC q l s n 
n n n n n n n n n n n p <return> q C-n C-n C-n C-n 
<return> <return> n n q l s L C-p C-p C-p C-p C-p C-p 
<return> C-g C-p C-p C-p C-p C-p C-p <return> 1 <return> 
C-. C-n C-n a C-x b <return> M-x r e p o r <tab> <
return>

Recent messages:
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Wrote /Users/ted/.newsrc
Wrote /Users/ted/.newsrc.eld
Wrote /Users/ted/.newsrc
Wrote /Users/ted/.newsrc.eld
Quit getting the articles to read
Quit
Loading emacsbug...done

-- 
Edward O'Connor
address@hidden

Ense petit placidam sub libertate quietem.