is_user_logged_in无法在premiumpress主题中工作

I'm having some problem with the function_is_user_logged_in. It can be seen on http://dev.cellarsale.co.za/index.php/listing/example-listing-2/ . I'm trying to make the "buy now" line disappear for unlogged people.

It's not working on my website for this part of code :

ob_start();  (...)

<table>
<tbody> (...)

<?php if(is_user_logged_in()){ ?> 

    <tr id="buynow" style="display: none;">

    <td colspan="5" class="bidbox biddingbox"> 

    <div class="wrap">

    <span class="label label-default pull-right" onclick="jQuery('.biddingbox').hide();" ><?php echo $CORE->_e(array('account','48')); ?></span>


    <hr />

    <form method="post" action="" class="row clearfix" onsubmit="return CheckBidding();">
    <input type="hidden" name="auction_action" value="newbid" />
    <input type="hidden" name="bidtype" value="bid" />
    <input type='hidden' name='hidden_cp' id='hidden_cp' value='<?php echo $current_price; ?>' />

     <div class="col-md-4">
     <div class="txtb"><?php echo $CORE->_e(array('auction','89')); ?></div>
     </div>
     <div class="col-md-4">         
        <div class='input-group'>
        <input type='text' class='form-control' id='bid_amount' name="bidamount"  placeholder='<?php echo ($current_price+1); ?>' /> 
        <span class='input-group-addon'><?php echo $GLOBALS['CORE_THEME']['currency']['symbol']; ?></span>
        </div>          
    </div>        
    <div class="col-md-2">        
        <button class="btn btn-lg btn-primary" type="submit"><?php echo $CORE->_e(array('auction','66')); ?></button>        
    </div>

    </form>

    <script>
    function CheckBidding(){        
    <?php 

    if($userdata->ID && ($userdata->ID == $post->post_author && $userdata->ID != 1) ){ ?> 

    alert("<?php echo $CORE->_e(array('auction','72','flag_noedit')); ?>"); return false; 

    <?php }elseif($userdata->ID){ ?>

        var bidprice = jQuery('#bid_amount').val();
        var ecp = jQuery('#hidden_cp').val();   
        var ecp = Math.round(parseFloat(ecp)*100)/100;
        var bidprice = Math.round(parseFloat(bidprice)*100)/100;

        if(jQuery.isNumeric(bidprice) && bidprice > ecp){   
            return true;
        }else{
        alert('<?php echo $CORE->_e(array('auction','73','flag_noedit')).' '.$GLOBALS['CORE_THEME']['currency']['symbol']; ?>'+ecp+'');
        return false;
        }

    <?php }else{ ?>

        alert("<?php echo $CORE->_e(array('auction','56','flag_noedit')); ?>"); return false;

    <?php } ?>

    };
    </script>

    <hr />

    <h4><?php echo $CORE->_e(array('auction','20')); ?></h4>

    <?php echo $CORE->_e(array('auction','90')); ?>

    <hr />
    <p><?php echo $CORE->_e(array('auction','65')); ?></p>

    <textarea><?php echo stripslashes($GLOBALS['CORE_THEME']['auction_terms']); ?></textarea>


    </div>

    </td>
    </tr>        
    <?php } ?> 
<?php } ?>        


  </tbody>
</table>

<?php 
// RETURN OUTPUT
$output = ob_get_contents();
ob_end_clean();
return $output;

I think the ob_start() at the beginning might be the reason why it's not working but the thing is I used is_user_logged_in just above and it worked. I also tried to put all the content in the "if(is_userlogged_in)" : it was still working for the first part but not for the one just above.

I also tried at one point to hide it with css just to check using the code below:

It didn't work at all, for logged or unlogged people.

Does someone has any ideas please ?