If you manually enter the date then click save it reverts to 01/01/1900. However if you manually enter the date then click that date on the calendar pop-up then click save it works. There's no prompt to click the date square on the calendar after you've entered the date in the date field as it appears to be an unnecessary step as it's already highlighted. It might be worth adding a line text somewhere in the calendar stating 'please click the calendar date to add' or similar.