Unusual behavior from git describe

I've encountered some strange behavior from git describe. Immediately after building my python project with setuptools tools git describe seems to think that the working tree is dirty. However after running git status (and seeing that nothing has changed) and running describe again the dirtyness seems to have disappeared. Any ideas as to what might be going on here?

git is version 1.7.3.2 on Mac OSX.  The full transcript is below.

Thanks in advance, Allan

% git describe --tags --dirty v0.0.3

% python ./setup.py sdist running sdist running egg_info writing requirements to flaskapi.egg-info/requires.txt writing flaskapi.egg-info/PKG-INFO writing top-level names to flaskapi.egg-info/top_level.txt writing dependency_links to flaskapi.egg-info/dependency_links.txt writing entry points to flaskapi.egg-info/entry_points.txt reading manifest file 'flaskapi.egg-info/SOURCES.txt' reading manifest template 'MANIFEST.in' writing manifest file 'flaskapi.egg-info/SOURCES.txt' warning: sdist: standard file not found: should have one of README, README.txt warning: sdist: missing required meta-data: url creating flaskapi-0.0.3 creating flaskapi-0.0.3/flaskapi creating flaskapi-0.0.3/flaskapi.egg-info creating flaskapi-0.0.3/flaskapi/apidoc creating flaskapi-0.0.3/flaskapi/testing creating flaskapi-0.0.3/tests creating flaskapi-0.0.3/tests/integration creating flaskapi-0.0.3/tests/unit creating flaskapi-0.0.3/tests/unit/testing making hard links in flaskapi-0.0.3... hard linking MANIFEST.in -> flaskapi-0.0.3 hard linking RELEASE-VERSION -> flaskapi-0.0.3 hard linking fabfile.py -> flaskapi-0.0.3 hard linking setup.cfg -> flaskapi-0.0.3 hard linking setup.py -> flaskapi-0.0.3 hard linking version.py -> flaskapi-0.0.3 hard linking flaskapi/__init__.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/app.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/base_view.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/errors.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/helpers.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/make_app.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi/registered_view_metaclass.py -> flaskapi-0.0.3/flaskapi hard linking flaskapi.egg-info/PKG-INFO -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/SOURCES.txt -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/dependency_links.txt -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/entry_points.txt -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/not-zip-safe -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/requires.txt -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi.egg-info/top_level.txt -> flaskapi-0.0.3/flaskapi.egg-info hard linking flaskapi/apidoc/__init__.py -> flaskapi-0.0.3/flaskapi/apidoc hard linking flaskapi/testing/__init__.py -> flaskapi-0.0.3/flaskapi/testing hard linking flaskapi/testing/base_api_test.py -> flaskapi-0.0.3/flaskapi/testing hard linking flaskapi/testing/json_helpers.py -> flaskapi-0.0.3/flaskapi/testing hard linking flaskapi/testing/json_requester.py -> flaskapi-0.0.3/flaskapi/testing hard linking tests/__init__.py -> flaskapi-0.0.3/tests hard linking tests/integration/__init__.py -> flaskapi-0.0.3/tests/integration hard linking tests/unit/__init__.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/test_base_view.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/test_errors.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/test_helpers.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/test_make_app.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/test_registered_view_metaclass.py -> flaskapi-0.0.3/tests/unit hard linking tests/unit/testing/__init__.py -> flaskapi-0.0.3/tests/unit/testing hard linking tests/unit/testing/test_base_api_test.py -> flaskapi-0.0.3/tests/unit/testing hard linking tests/unit/testing/test_json_helpers.py -> flaskapi-0.0.3/tests/unit/testing copying setup.cfg -> flaskapi-0.0.3 Writing flaskapi-0.0.3/setup.cfg tar -cf dist/flaskapi-0.0.3.tar flaskapi-0.0.3 gzip -f9 dist/flaskapi-0.0.3.tar tar -cf dist/flaskapi-0.0.3.tar flaskapi-0.0.3 gzip -f9 dist/flaskapi-0.0.3.tar removing 'flaskapi-0.0.3' (and everything under it)

% git describe --tags --dirty v0.0.3-dirty

% git status # On branch master nothing to commit (working directory clean)

% git describe --tags --dirty v0.0.3