Django Model.objects.all().delete() not completing

I have a django app which deletes all the entries in a db and then enters another set. I am having a problem where Model.objects.all().delete() leaves objects in the database (The same entries every time).

I have fixed it using this code:

db_events = Event.objects.all()
while db_events.count():
    db_events.delete()

Clearly this is not a great fix. What is going on and how can I fix it?