unexpected behavior with `**` patterns

[azdavis]

repo with test case here: https://github.com/azdavis/wax-trouble

tldr is: given this directory structure:

testing
\ _ a
    \ _ foo.txt
\ _ b
    \ _ foo.txt

and this rust code:

#[test]
fn hm() {
    let all_foo = "**/foo.txt";
    let pwd = std::env::current_dir().unwrap();
    let testing_dir = pwd.join("testing");
    let testing_dir = testing_dir.as_os_str().to_str().unwrap();
    let glob_rooted_at_dir_walk_anything: Vec<_> = go(&format!("{testing_dir}/{all_foo}"), ".");
    let glob_un_rooted_walk_in_dir: Vec<_> = go(all_foo, &testing_dir);
    assert_eq!(glob_rooted_at_dir_walk_anything, glob_un_rooted_walk_in_dir);
}

pub fn go(glob: &str, walk: &str) -> Vec<std::path::PathBuf> {
    wax::Glob::new(glob)
        .unwrap()
        .walk(walk)
        .map(|x| x.unwrap().into_path())
        .collect()
}

i would expect the test to pass but it does not. it fails with:

thread 'hm' panicked at src/lib.rs:9:5:
assertion `left == right` failed
  left: []
 right: [".../wax-trouble/testing/a/foo.txt", ".../wax-trouble/testing/b/foo.txt"]

where ... is the absolute path containing the repo.

i would not expect the lhs (glob_rooted_at_dir_walk_anything) to be empty. i would expect it to be the same as the rhs (glob_un_rooted_walk_in_dir).