error "Not a valid object name" filtering an ex-svn git repo with renames

Under git version 1.5.4.3, which as of writing is the current in ubuntu 8.04 hardy heron, trying to split out a folder from a git repo where the repo was an import from subversion (svn), and the folder was renamed in the past causes a failure as show below:

#!/bin/bash -v
rm -rf test-case
mkdir test-case
cd test-case/
svnadmin create svnrepo
export repo="`pwd`/svnrepo"
mkdir -p import/a
echo '1' >> import/a/file.txt
svn import -m 'initial import' import file://$repo/trunk/
svn co file://$repo/trunk/ checkout
echo '2' >> checkout/a/file.txt
svn ci -m "file modified" checkout
svn mv -m "moving file" file://$repo/trunk/a file://$repo/trunk/b
svn up checkout
echo '3' >> checkout/b/file.txt
svn ci -m "modified again" checkout
svn log -v checkout
mkdir -p gitcopy/a
git svn clone file://$repo/trunk/ gitcopy/a
cd gitcopy/a
git filter-branch --subdirectory-filter a #fails [1]
cd ../../
mkdir gitcopy/b
git svn clone file://$repo/trunk/ gitcopy/b
cd gitcopy/b
git filter-branch --subdirectory-filter b

The marked line above fails with the following error:
[1] Rewrite bcfe73ef303832b6112a2419dc1da5f782672c14 (3/3)fatal: Not a valid object name bcfe73ef303832b6112a2419dc1da5f782672c14:a

This has been fixed in the latest build of git: version 1.6.0.1.294.gda06a and no longer fails.

The "fatal: Not a git repository" error message that filter branch produces doesn't seem to matter.