p:ajax update of more than one element - ajax

Question

I'm having trouble when trying to update two elements.
This is my code:
<h:form id="all">
<table id="gt" class="CartContents Stylize General" cellspacing="0" cellpadding="0" style="display:#{clothesBean_i.convertToList(clothesBean_i.cartclothes)}">
<tbody>
<!-- AFFICHAGE PRODUIT -->
<ui:repeat value="#{clothesBean_i.convertToList(clothesBean_i.cartclothes)}" var="c">
<tr>
<td class="CartThumb" style="">
<img src="" /> 
</td>
<td class="ProductName" colspan="1">
<h5></h5>
<br />
</td>
<td align="center" class="CartItemIndividualPrice">
$ #{c.price}
</td>
<td id="qt" align="center" class="CartItemIndividualPrice">
<h:outputLabel for="ajaxSpinner" value="" />
<p:outputPanel id="mypanel">
<p:spinner id="ajaxSpinner" value="#{clothesBean_i.qt}" min="1" max="100">
<p:ajax update="tot grandT" process="#this" />
</p:spinner>
</p:outputPanel>
</td>
<td align="center" class="CartItemIndividualPrice">
<h:outputText id="tot" value="$ #{clothesBean_i.getClothePriceQt(c)}" />
</td>
</tr>
</ui:repeat>
</tbody>
<tfoot >
<tr class="SubTotal GrandTotal">
<td colspan="4">Grand Total:</td>
<td >
<h:outputText id="grandT" value="$ #{clothesBean_i.getClothesPrice(clothesBean_i.convertToList(clothesBean_i.cartclothes))}" />
</td>
</tr>
</tfoot>
</table>
</h:form>
in this line
<p:ajax update="tot grandT" process="#this" />
when I give just one id (tot or grandT) it works fine,
but with two ids I just get a blank page (nothing is showing)!