date_select validate all fields selected

Hi,

date_select seems to behave rather strangely if :prompt => true or :empty => true and the user does not select all fields.

It seems that by the time the birth_date field gets to validation, its filled with a Date object that has defaults set for empty fields. eg If a year is selected but month and day are not, then month and day are set to january 1st. This is really not intuitive but I'm still new to rails (made the move from CakePHP at last!) - maybe I'm doing something wrong.

Is there a best practice here that I don't know about?

Thanks!