activeRadioButtonList and bool values

Trying something like this ( Yii PHP framework 1.1 alpha )

echo CHtml::activeRadioButtonList( $form, "day"

, array( false=>"night", true=>"day" ) );

where

$form->day = true;

neither button is selected

get value=0 and value=1 in html

Is this a bug or am I doing it wrong ?

Any guidance appreciated.