Bug in update-index?

Hi, the following bombs out:

 time git --work-tree=/usr/local/texlive/2007/texmf-dist ls-files -z -m -o .|git --work-tree=/usr/local/texlive/2007/texmf-dist update-index --add -z --stdin
error: bibtex/bib/IEEEtran/IEEEabrv.bib: does not exist and --remove not passed
fatal: Unable to process path bibtex/bib/IEEEtran/IEEEabrv.bib

It would appear that update-index is not finding the listed file in spite of the --work-tree argument.