Yii 1.x - 必填字段保存为空

I have a field set as required in the model, yet I have seen users saving it as an empty string (ie. ''). When I tested it, I do receive the "Cannot be blank" message properly, so don't know how to prevent this in the future. Do I have to specify all scenarios in the rule (eg, 'insert', 'update')? By the way, I tried updating the field, and it doesn't let me save it empty (I even tries spaces).

These are the rules applied on the field (model):

public function rules()
{
    return array(
        array('field', 'required'),
        array('field', 'length', 'max'=>4096),
        array('field', 'safe', 'on'=>'search'),
    );
}

For @RiggsFolly :) the controller action:

public function actionUpdate($id)
{
    $model = Model::model()->findByPk($id);

    $formData = Yii::app()->request->getPost('Model'); 

    if ($formData)
    {

        $model->attributes = $formData;
        $model->save(); 
    }

    $this->render('update',array(
        'model'=>$model
     ));
}

... and the view:

<?php $form=$this->beginWidget('CActiveForm', array(
    'id'=>'form'
)); ?>

<?php echo $form->textArea($model,'text',array( 'rows'=>5 ')); ?>

<?php $this->endWidget(); ?>

Can you imagine any scenario this field could be saving an empty string in the database?