Hm.  I *was* using darcs-2pre when this corruption happened.  So this may be a
bug in darcs-2pre, which results in a repository such that both darcs-2pre and
darcs-1.1.0pre exhibit the same behavior when faced with that repository.

By the way, since this is potentially interfering with the http://allmydata.org
project (for example, I wanted to look at a patch today and instead got this: 
http://allmydata.org/trac/tahoe/changeset/2230/src/allmydata/webish.py ), I
might try to perform surgery on my repository to erase the patches that touched
darcsver-1.1.1.tar.gz file from history.  Fortunately, those patches were a
brief mistake and are not used or required by any other patch...