Creating a relationship using the API returns start date and end date in a wrong format

If I create a relationship like this:

drush cvapi Relationship.create sequential=1 contact_id_a=45 contact_id_b=1 relationship_type_id=5 start_date="2004-06-02"

I get:

Array
(
[is_error] => 0
[version] => 3
[count] => 1
[id] => 12619
[values] => Array
(
[0] => Array
(
[id] => 12619
[contact_id_a] => 45
[contact_id_b] => 1
[relationship_type_id] => 5
[start_date] => 20040602000000
[end_date] => NULL
[is_active] => 1
[description] =>
[is_permission_a_b] => 0
[is_permission_b_a] => 0
[case_id] =>
)
)
)

The returned start date is in the wrong format: 20040602000000 instead of 2004-06-02 (which is the correct format, I presume). If I get the relationship afterwards, the result is correct:

drush cvapi Relationship.getsingle sequential=1 id=12619
Array
(
[id] => 12619
[contact_id_a] => 45
[contact_id_b] => 1
[relationship_type_id] => 5
[start_date] => 2004-06-02
[is_active] => 1
[description] =>
[is_permission_a_b] => 0
[is_permission_b_a] => 0
)