sparse checkout - weird behavior

Here's a simple reproducible bug - something unexpected in sparse-checkout mode:

  $ git clone git@github.com:jekyll/jekyll.git --no-checkout
  Cloning into 'jekyll'...
  remote: Counting objects: 41331, done.
  remote: Compressing objects: 100% (5/5), done.
  remote: Total 41331 (delta 0), reused 0 (delta 0), pack-reused 41326
  Receiving objects: 100% (41331/41331), 11.91 MiB | 7.98 MiB/s, done.
  Resolving deltas: 100% (26530/26530), done.
  $ cd jekyll
  $ ls
  $ git config core.sparsecheckout true
  $ echo 'docs*' > .git/info/sparse-checkout
  $ git read-tree -mu HEAD
  $ ls
  docs rake

I didn't expect to see 'rake' amongst the results.

If I take out the asterisk on the echo line, only 'docs' is checked out after the read-tree operation. Even if asterisk isn't allowed, I'd not expect it to fail in that way. Sparse checkout documentation is a little . .. . sparse it has to be said (sorry).

As it happens, I have some more complicated cases where sparse-checkout is doing the wrong thing in the working copy - and I'll work towards reproduction of that/those after this. Best to start with a simple reproducible case in case there's a simple fix for more that one similar bug.

Regards,

- Paul