Shell script mode does not re-color the buffer when changing shell

["Göran Uddeborg" <uddeborg@carmen.se>]

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In GNU Emacs 21.3.1 (x86_64-redhat-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2005-02-04 on thor.perf.redhat.com
configured using `configure  --build=x86_64-redhat-linux --host=x86_64-redhat-linux --target=x86_64-redhat-linux-gnu --program-prefix= --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --with-pop --with-sound'
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: nil
  default-enable-multibyte-characters: t

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

If I have a buffer in shell script mode which already has syntax
coloring on, and I change the shell, the syntax coloring is still from
the original shell.

Repeat by:

1. Invoke emacs with font lock enabled by default (and an otherwise
   minimal environment):

   env -i SHELL=/bin/tcsh DISPLAY=$DISPLAY HOME=$HOME emacs -q -f global-font-lock-mode

2. Visit file "apa.sh":

   C-x C-f apa.sh

   This buffer is following the rules for tcsh.  If I type "foreach"
   on a line, it is colored as a keyword, but if I type "for" it is
   just black.  So far so good.

3. Change shell to bash (for example):

   C-c : /bin/bash

   The mode line changes to bash, and indentation rules adapt.  But
   colorisation is still according to tcsh.  "foreach" is still
   colored, and "for" is not.  This is true both for the already
   existing occurrences, and if I enter the words again.

I would expect coloring to change together with other aspects of the
mode.

Recent input:
C-x C-f a p a . s h <return> f o r e a c h <return> 
f o r <return> C-c : / b i n / b a s h <return> f o 
r e a c h <return> f o r <return> M-x r e p o r t - 
<return>

Recent messages:
Loading sh-script...
Loading easy-mmode...done
Loading sh-script...done
No indentation for this shell type.
Magic number changed to `#! /bin/bash'
Setting up indent for shell type bash
setting up indent stuff
Indentation variable are now local.
Indentation setup for shell type bash
Loading emacsbug...done