git ls-files --error-unmatch weirdness

Hi,

I was looking for untracked files when noticed this:

repo$ git init
Initialized empty Git repository in /home/szeder/tmp/git/repo/.git/
repo (master)$ mkdir dir
repo (master)$ touch dir/file
repo (master)$ git add dir/file
repo (master)$ git commit -m 'first'
[master (root-commit) 2c0990c] first
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 dir/file
repo (master)$ git ls-files --others --error-unmatch
repo/dir (master)$ echo $?
0
repo (master)$ cd dir
repo/dir (master)$ git ls-files --others --error-unmatch
error: pathspec '' did not match any file(s) known to git.
Did you forget to 'git add'?
repo/dir (master)$ echo $?
1

So, the same 'git ls-files' command is OK when run at the top of the worktree, but errors out in a subdirectory. What's going on? Is this a bug? If not, why not?

Thanks, Gábor