[BUG] git-add doesn't apply filepatterns to tracked files

Ran across a rather bizarre bug today while trying to help someone in #git.
It seems that git-add doesn't match filepatterns against tracked files,
only against untracked files. Other tested commands (such as git-rm and
git-ls-files) are happy to match tracked files, but not git-add.

% git --version
git version 1.7.3.3.576.gd872
% ls -a
./       ../      .git/    bar.txt  foo.txt
% git status --short
 M foo.txt
?? bar.txt
% git add '*.txt'
% git status --short
A  bar.txt
 M foo.txt

There are no .gitignores in play here.

I haven't had time to investigate the source yet, as I'm still at work.

-Kevin Ballard