Geo importer complains about duplicate stats areas on successive imports

[tituomin]

./manage.py geo_import --divisions helsinki

django.db.utils.IntegrityError: duplicate key value violates unique constraint "munigeo_administrativedivision_ocd_id_key"
DETAIL: Key (ocd_id)=(ocd-division/country:fi/tilastoalue:2351003006) already exists.