This should not be the case. Is the field empty or does it already have data when you drop down the calendar and you see this behavior?
Is the date field a field of type date or some other type such as text when you check it's field type in Manage | Database | Fields?
It is a field that I first selected as a drop down list to select the month of the year. I decided to change it to a drop down calendar to enable me to select the day of the month. I changed the field from Number to Date, and now it works.
Thanks for the response.