[DatePickerRange] Persistence with defaut values

I’m experiencing an unexpected behavior when using both default values for start_date and end_date and the persistence property set to True.
I would expect to have my default values the first time I visit the page, then the value I used the last time I was on the page.
However, I always see my default values being used.
Has anyone any idea why and how I can work around this behavior ?
Thanks =)