Bash string substitution bug (?)

[Dmitry V Golovashkin]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: x86_64-redhat-linux-gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-redhat-linux-gnu' 
-DCONF_VENDOR='redhat' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' 
-DSHELL -DHAVE_CONFIG_H  -I.  -I. -I./include -I./lib   -O2 -g -pipe -m64
uname output: Linux acl201.unx.sas.com 2.6.9-42.ELsmp #1 SMP Wed Jul 12 
23:32:02 EDT 2006 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-redhat-linux-gnu

Bash Version: 3.0
Patch Level: 15
Release Status: release

Description:
   unexpected bad substitution:
   enter the following simple list:

    prompt:  CLUSTER='1 2'; echo ${CLUSTER/${HOSTNAME%%.*}}
    output:       1 2

   the idea of the above line is to remove short HOSTNAME (without the 
trailing domain)
         from the CLUSTER - works fine (CLUSTER was assigned a dummy 
value - irrelevant)
   however the same operation with slash results in a bad substitution 
error.
   the substitution appears to be a valid one.

      prompt: CLUSTER='1 2'; echo ${CLUSTER/${HOSTNAME/.*}}
      output:             -bash: ${HOSTNAME: bad substitution
  

Repeat-By:

Fix: