touching a file causes it to be listed using git diff-files

If I touch a file in the working directory (only changing it's last-modified) attribute it shows up when running git diff-files.

If I then run git status followed by git diff-files again it doesn't show up either time.

Is this an error?

Simple example:

[dev]$ git --version git version 1.6.5.3

[dev]$ git init t Initialized empty shared Git repository in /Users/stephen/dev/t/.git/

[dev]$ cd t
[t (master)]$ echo 'hi' > hello; git add hello; git commit -am 'initial commit'
[master (root-commit) f39d21a] initial commit
  1 files changed, 1 insertions(+), 0 deletions(-)
  create mode 100644 hello

[t (master)]$ git diff-files

[t (master)]$ git status # On branch master nothing to commit (working directory clean)

[t (master)]$ touch hello

[t (master)]$ git diff-files :100644 100644 45b983be36b73c0788dc9cbcb76cbb80fc7bb057 0000000000000000000000000000000000000000 M hello

[t (master)]$ git status # On branch master nothing to commit (working directory clean)

[t (master)]$ git diff-files