html_select_date bug - maybe ?

smarty 2.5.0 I'm using html_select_date to enter peoples birth dates in my application. I understand the problem with epoch time and have used the format 'yyyy-mm-dd' to store in database/variable/etc and using a modified version of 'date_format' to present the date. However 'html_select_date' gives spurious date/month values pre 1970's eg giving 1945-02-01 to html_select_date displays 1945-01-01 Indeed anything pre 1970's seems to give spurios errors with the date or month values (year seems to be correct) Is this because the timestamp is not handled correctly or should I not be using html_select_date for pre 1970 ?? Hope it makes sense tia Pete