I have a custom form for updating a database row. I pre-populate the field values using $form->loadDataFrom( $data ), where $data is an associative array of the field values.

This works great for all but the DropdownField; nothing is set as "selected".

Relevant code:

On the form subclass:

$fields = FieldList::create(
...
DropdownField::create('subscribed')->setSource(array('1' => 'Yes', '0' => 'No'))->setAttribute('class', 'default')
);

In the controller:
$form->loadDataFrom($data);

I have verified that $data is a properly formatted associative array (after all, every other field gets the appropriate value).

The dropdown field will not set a selected value.