components/behaviors/CheckboxListBehavior.php
public function afterFind($event)
    {

        if (is_array($this->fields)) {
            foreach ($this->fields as $field) {
                if ($event->sender->{$field}) {
                    $event->sender->{$field} = explode(';', $event->sender->{$field});
                }
            }
        }

    }
public function afterFind($event)
    {

        if (is_array($this->fields)) {
            foreach ($this->fields as $field) {
                if ($event->sender->{$field}) {
                    $event->sender->{$field} = explode(';', $event->sender->{$field});
                }
            }
        }

    }
Change string separated by ; to array
@param $event