backtick expansion is truncated

[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 use a long backtick expansion, it is not all evaluated in some 
circumstances (but it apparently is if only using builtins).

Repeat-By:
for f in `seq 20000`; do ls /dev/null; done|wc -l
yields 4097, not 20000 that it should.  However,
for f in `seq 20000`; do echo /dev/null; done|wc -l
yields 20000 (presumably because of using the bash builtin echo)