title: django-simple-history is storing changes twice
body: <p>I tried django-simple-history and I discovered that every create or update is stored twice in the history model. I don't know which information is now useful for you to help me, but I use CBV's and model forms. I followed the instructions on how to install and setup and everything works fine. What I'm wondering is why there is a command line called clean_duplicate_history, which indeed removes all duplicates records. Thank you in advance for any help.</p>