We found this when the /tmp partition overflowed on our webserver that
uses the darcsweb cgi script. The /tmp contained lots of new-<project>
and old-<project> directories, and the same with -<n> added (with n form
1 to some two-digit number).

We can reproduce the bug by issuing

  darcs diff --from-patch=<some patch name>

and then hitting Ctrl-C fast; we need to try this a number of times
before the error occurs, it "helps" if the darcs diff is slow.

The version we use is darcs-2.4.4 (with later versions we still
regularly encounter http://bugs.darcs.net/issue1980).

I have looked at the source code and cannot detect anything that would
explain this. Also, I could not reproduce this problem on any other
machine here, except on the web server. It might be possible that the
darcs binary is not 100% compatible with the OS on the server (a SuSE
SLES 10); I copied a darcs binary compiled on a debian system to the
server machine, since I could not find binary rpms for SLES 10.