Date picker issue

[ilfungo]

Hi I need to register the customer birthday date during the customer registration. However when the datepicker pops up the only permitted date are in the current year and in the future one. I couldn't  find where to change the parameter. I had to work around by the code, but I changed a core function and this is not the right procedure. I had to go in administrator/components/com_virtuemart/helpers/vmjsapi.php and comment the '.$minMax.' paramether in the the self::addJScript('datepicker',' etc function. How can I solce the issue in a nice and clean way? I think this is a bug.