Empty POST DATA

server with php 5.4. Codeigniter 3.1.0. Xss false.

Posting data from form code below :

PHP Code:

<?echo form_open('/administration/gestione_blocco/aggiorna_blocco');?>
            
        <p>
                <label><?=$this->lang->line('Contenuto')?> <?=$this->lang->line('colonna')?> 1</label>
                <textarea id='contenuto1' class='text-input html' name='contenuto1'><?=$blocks[0]->contenuto1?></textarea>
            </p>
            <p>
                <label><?=$this->lang->line('Contenuto')?> <?=$this->lang->line('colonna')?> 2</label>
                <textarea id='contenuto2' class='text-input html' name='contenuto2'><?=$blocks[0]->contenuto2?></textarea>
            </p>
            
            <p>
                <input type='submit' class='button' value='Aggiorna'/>
            </p>
            <!--</form>-->
            <?echo form_close();?>

if in the field contenuto1 i type something like this

PHP Code:

<p>Pippo</p> 


all work fine.
But if in the field contenuto1 i type something like this

PHP Code:

<p><b>Pippo</b></p> 


in the controller i get empty post data.
Anyone knows why?