bug report: `git stash save -u` deletes directory whose contents are .gitignored

hi,

- `git stash save -u` deletes a directory, even though the _contents_
of that directory are .gitignored (e.g. "foo/*" in .gitignore).
Detailed reproduction below.
- The behaviour is not present when instead .gitignoring the directory
itself (e.g. "foo"). This does imo not excuse the behaviour of the
described case.
- The behaviour is not present with just `git stash save`.
- The expected behaviour is: Only files listed in `git status` are
stashed away; other things are left untouched. Potential exception:
empty directories.
- I am aware that `git stash save -u` is supposed to have semantics
involving the equivalent of `reset --hard` and `clean -f`. Neither of
those expose the directory-deletion behaviour.

additional comments, not directly relevant to this bug:
- both `git stash save; git stash pop` and `git stash save -u; git
stash pop` should ideally behave as an "identity effect". The latter
might affect the index (i.e. have an effect equivalent to `git reset`
or something in that direction). Any other effect / special cases are
bad interface design imo. If a differing design was chosen on purpose,
i am thankful for pointers on the reasoning.
- no, i luckily did not truely lose files due to the current behaviour.

lennart

----

reproduction:

git init

Initialized empty Git repository in $SOMEDIR/.git/

mkdir ignore-contents
echo "ignore-contents/*" > .gitignore
git add .gitignore
git commit -m "initial" > /dev/null
touch ignore-contents/blah.txt
touch abc.txt
git status

On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

  abc.txt

nothing added to commit but untracked files present (use "git add" to
track)

ls -1a

.
..
abc.txt
.git
.gitignore
ignore-contents

git stash save -u

Saved working directory and index state WIP on master: adc468b initial
HEAD is now at adc468b initial

ls -1a

.
..
.git
.gitignore

git stash pop &> /dev/null
ls -1a

.
..
abc.txt
.git
.gitignore

git --version

git version 2.6.1