git commit --verbose shows incorrect diff when pre-commit hook is used to modify files

Hi,

I am trying to use a pre-commit hook to modify files before they are
to be committed. The problem I am running into is that if I use "git
commit --verbose", which I often do so that I can see the diff, the
diff it displays in the editor is the diff before the pre-commit hook
was run rather than what the diff would be after the pre-commit was
run.

I would like to note, that the pre-commit hook is definitely running,
but when git grabs the diff seems to be in the wrong place.

I have set up a simple example on my github to show the problem.
https://github.com/fchorney/pre-commit-example

Is this intended behaviour, or perhaps an issue?

 Thanks,
 Fernando Chorney