git-am with an initial checkin doesn't work

Hi,

I've a question concerning 'git am' and 'git format-patch'. It seems
impossible to apply the "initial checkin" (as generated by git
format-patch -N --root) to an empty repository. The following workflow
might clarify that:

# Create a new repository with an initial checkin:
mkdir foo && cd foo && git init
echo "initial checkin" > initial.checkin
git add initial.checkin && git commit -m "initial checkin"

# Kinda "export" the repo:
git format-patch -1 --root; # generates 0001-initial-checkin.patch

# Re-create the repository:
rm -rf .git initial.checkin && git init

# Try to "import" the patch:
git am 0001-initial-checkin.patch

The latter yields to
fatal: HEAD: not a valid SHA1
fatal: bad revision 'HEAD'

It works, when I
git apply 0001-initial-checkin.patch
instead of am'ing it, but then the thing isn't committed and I've to
manually git-commit it.

Is this a bug, intentional behavior, or am I missing some magic option
to git-am?

Background:
I faced that problem when I tried to import some old data into Git
(namely .tar.gz files) and wanted to start with 2 or 3 commits of my own
(the import scripts) and then the other files on top of it. Because my
import scripts didn't work well at first, I had to re-, re-, and
re-import and start over all again. To always start with a clean repo, I
thought adding my scripts and then saving them as 000N-*.patch would be
a good idea, but the initial git-am didn't work. I know, there are other
ways (git-rebase is a big friend here), but I thought git-format-patch
and git-am worked symmetrically. Wrong?

Cheers,
    Dirk