The change

Mon Feb 18 11:43:11 EST 2008  David Roundy <droundy@darcs.net>
  * resolve issue673: if hash check fails, try reading file without ungzipping it.

should fix a bug relating to adding of gzipped files to the repository.  This
only affects hashed and darcs-2-format repositories.  Old-style repositories
shouldn't be affected at all (because their pristine cache isn't compressed).

I am unable to access http://allmydata.org/source/darcs/trunk-reget, but from
what you describe (adding and removing gzipped tarball), I believe the
corruption is consistent with what could have been created prior to this bug
fix... or possibly it would require that the second patch is recorded after the
bugfix (I'm not sure).

I'm marking this bug as resolved, since I think we've resolved it.  Thanks for
your patience in tracking this down!

David