Sparse worktree always contains root files

Hi there,

I'm trying to use sparse checkouts in a large project, and one oddity
(bug?) came up.

If I do a normal full clone of a repository, then do:
    git worktree add ../sparse --no-checkout
    cd ../sparse
    git sparse-checkout set somepath
    git checkout
Now indeed it is a sparse worktree, but the files from the root
directory are also there.

This also happens with traditional (non-worktree) partial clones.
(I did both shallow, blob-less and tree-less, and all of them behave
the same way)

Regards,
-Jeppe