civicrm_api3_membership_create() php API sets join_date and start_date to 0000-00-00

PARAMS:
Array (
[contact_id] => 1
[membership_type_id] => 3
[join_date] => 2011-09-05
[start_date] => 2011-09-05
[end_date] => 2013-09-05
[source] => Course
[is_override] => 0
[status_id] => 2
[version] => 3
)

RESULT:
Array (
[is_error] => 0
[version] => 3
[count] => 1
[id] => 5
[values] =>
Array (
[5] =>
Array (
[id] => 5
[contact_id] => 1
[membership_type_id] => 3
[join_date] => 2011-09-05
[start_date] => 2011-09-05
[end_date] => 20130905
[source] => Course
[status_id] => 2
[is_override] => null
[reminder_date] => null
[owner_membership_id] =>
[is_test] =>
[is_pay_later] =>
[contribution_recur_id] =>
[campaign_id] =>
)
)
)

SQL DUMP:
id contact_id membership_type_id join_date start_date end_date source status_id is_override reminder_date owner_membership_id is_test is_pay_later contribution_recur_id campaign_id
4 1 3 0000-00-00 0000-00-00 1970-01-01 Course 2 NULL NULL NULL 0 0 NULL NULL