incomplete execution in long backtick expansion

[Brian Minton]

Configuration Information [Automatically generated, do not change]:
Machine: i486
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i486'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i486-pc-linux-gnu'
-DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash'
-DSHELL -DHAVE_CONFIG_H   -I.  -I../bash -I../bash/include
-I../bash/lib   -g -O2
uname output: Linux bminton.is-a-geek.net 2.6.15.4 #0 SMP Sat Feb 18
12:04:34 EST 2006 i686 GNU/Linux
Machine Type: i486-pc-linux-gnu

Bash Version: 3.1
Patch Level: 5
Release Status: release

Description:
If I have a long command line expansion with back ticks,
executing code in a for loop, the contents of the loop are not
executed every time.  This does not seem to be true for built-in
commands inside the loop.

Repeat-By:
for f in `seq 20000`; do ls /dev/null;done|wc -l
(output: 4097)
for f in `seq 20000`; do echo /dev/null;done|wc -l
(output: 20000)
for f in `seq 20000`; do /bin/echo /dev/null;done|wc -l
(output: 4097)