I don't know if that could possibly make
a difference but if I select New Record then the field will show the correct
date. It is only when the form is first opened and a blank record is
displayed.
It sounds like there is a record (the first record in the form's
recordsource), actually stored in the table, with the date the record was
created in this field and NULL values in all the other fields. Since it's an
existing record the Default Value will not apply.
Perhaps you should just delete this record if it does not contain any useful
data. Then you'll see the first "real" record (first in terms of the sort
order of the recordsource, which might or might not be chronological), with
whatever date that record contains.