[ Edited resend from
  http://lists.gnu.org/archive/html/emacs-devel/2008-05/msg00349.html ]

Type the following after M-x eshell RET:

echo "1+1" | bc

and then the return key. Instead of the expected answer 2, eshell
displays:

bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.

now type the return key again. Here the answer is shown:

2

type the return key again. Nothing happens. Eshell blocks. Control-C
shows:

(interrupt) use quit to exit.


In GNU Emacs 23.0.60.3 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2008-05-06 on golem
Windowing system distributor `The X.Org Foundation', version 11.0.70000000
configured using `configure  '--enable-font-backend--with-gtk'
'--with-gif=no''