git add -N. && git commit -m foo creates empty commits

gistfile1.sh

$ git --version
git version 1.8.5.rc2.7.g8167612              # same behavour with 1.9.1.423.g4596e3a

$ git init
Initialized empty Git repository in /home/torstein/tmp/git-empty/.git/

$ echo "f" >file

$ git add file

$ git commit -m 1
[master (root-commit) 2871899] 1
 1 file changed, 1 insertion(+)
 create mode 100644 file

$ git commit -m 2                             # git won't let me create an empty commit
On branch master
nothing to commit, working directory clean

$ git commit -m 2 --allow-empty               # unless I give --allow-empty
[master cd018ba] 2

$ echo "b" >file2

$ git add -N .

$ git commit -m 3                             # This creates an empty commit, without --allow-empty
[master 2690e42] 3

$ git show
commit 2690e42a7381c80cfcc86caaf5d3f2c60f47ab78 (HEAD, master)
Author: Torstein Hegge <hegge@resisty.net>
Date:   Thu Mar 20 13:55:02 2014 +0100

    3

$ git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        new file:   file2

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   file2