Not really important since it is a nonsense operation, but darcs insists 
that it's a bug that should be reported, so here we go.

Steps to reproduce as a console log:

moos@l04:~$ mkdir t
moos@l04:~$ cd t
moos@l04:~/t$ darcs init
moos@l04:~/t$ darcs pull
darcs: bug in darcs!
Impossible case at Pull.lhs:194 compiled 11:27:12 Apr  5 2006
Please report this to bugs@darcs.net,
If possible include the output of 'darcs --exact-version'.

darcs --exact-version says:

darcs compiled on Apr  5 2006, at 11:28:49
# configured Tue Feb 28 07:02:39 EST 2006
./configure --no-create --no-recursion

Context:

[TAG 1.0.6
Tommy Pettersson <ptp@lysator.liu.se>**20060228111841]

This is on an AMD 64 running Kubuntu Hoary Hedgehog, darcs is compiled 
with the binary x86_64 tarball build of ghc version 6.4.1. If that matters 
:)

Great program, BTW.

Fixed in 1.0.8.