form checkbox #default_value messing

Hello
I cannot get the checkbox to reflect its value in db.(0,1)$form['activated'] = array(  '#type' => 'checkbox',  '#title' => t('activate this period.'),  '#description' => t('activate this period'),  '#default_value' =>  !empty($holidays)? $data->activated :1,); 
My sql field is an int(10).
and $data->activated returns 0 or 1.
why my box gets stuck? I can write its value but not read it!
Any opinion is welcome...