Expected behaviour for pathspecs matching attributes in subdirectories

Hi,

I'm working with pathspecs matching on attributes, here's a basic repo setup:

    $ git init .
    $ mkdir -p sub/sub
    $ touch fileA sub/fileA sub/sub/fileA
    $ echo 'fileA labelA' > sub/.gitattributes
    $ git add .
    $ git commit -m 'Build the repo'

What I want to do: list all files under 'sub/sub' that have 'labelA' as an
attribute.

Working from the top level I get the output I would expect:

    $ git ls-files -- ':(attr:labelA)'
    sub/fileA
    sub/sub/fileA
    $ git ls-files -- ':(attr:labelA)sub'
    sub/fileA
    sub/sub/fileA

But as soon as a directory is included in the pathspec's path no files are
returned:

    $ git ls-files -- ':(attr:labelA)sub/'
    $ git ls-files -- ':(attr:labelA)sub/sub'

Without the attribtue magic I can use a directory to list files there:

    $ git ls-files -- sub/sub
    sub/sub/fileA

Is this the expected behaviour? I looked in t/t6135-pathspec-with-attrs.sh and
didn't see a test case covering something similar. If this is expected, is
there another way to achieve what I'm looking for?

Thanks for your time,
Matt