git stash and manually edited chunks

Hi!
I asked a question on stackoverflow
(http://stackoverflow.com/questions/4058372/git-stash-and-edited-chunks)
and someone suggested it might be a bug...
For convenience, I reproduce the question here:

 I occasionally have the following problem, which is reproduced by the
following sequence of commands:

* git add -p my_file
* I edit a chunk *manually* (using e)
* git stash --keep-index
* git stash pop

Now the problem occurs: the file my_file is now considered as
conflicted, and git has completely messed with my edited chunk, so I
have to edit the file, remove the merge marks, and run git add my_file
followed by git reset HEAD

I'm puzzled because this happens only when editing a chunk manually. I
don't see how this should make any difference at all.

I'm using version 1.7.3.1 on Mac OS X.

Thanks!!