IFS=: breaks literal patterns with character classes

[Enrique Perez-Terron]

Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i386' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i386-redhat-linux-gnu' 
-DCONF_VENDOR='redhat' -DLOCALE
DIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H   -I.  -I. 
-I./include -I./lib  -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 
-O2 
-g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector 
--param=ssp-buffer-size=4 -m32 -march=i586 -mtune=generic 
-fasynchronous-unwind-tables
uname output: Linux apeiron.home.lan 2.6.29.4-167.fc11.i586 #1 SMP Wed May 27 
17:14:37 EDT 2009 i686 i686 i386 GNU/Linux
Machine Type: i386-redhat-linux-gnu

Bash Version: 4.0
Patch Level: 23
Release Status: release

Description:
        See the Repeat-by section. Character class [:graph:] appears not to 
match as it
        should, if IFS=':'.  Why, or at what stage, is IFS used here? 

Repeat-By:
        $ # Correct:
        $ (IFS=' '; case A in ([[:graph:]]) echo graph;; (*) echo non-graph;; 
esac)
        graph

        $ # Not correct:
        $ (IFS=':'; case A in ([[:graph:]]) echo graph;; (*) echo non-graph;; 
esac)
        non-graph

        $ # Contrast with
        $ (IFS=:; echo a:b)
        a:b

        $ # The error also happens with the == operator:
        $ # Correct:
        $ (IFS=' '; [[ A == [[:graph:]] ]] && echo yes || echo no)
        yes

        $ # Not correct
        $ (IFS=':'; [[ A == [[:graph:]] ]] && echo yes || echo no)
        no