jesi template caching problem

Hi everybody,
 
I have a question regarding the jesi caching
 
I created the following jsp:
 
<%@ taglib uri="/WEB-INF/etc/taglibs/jstl/c" prefix="c" %>
<%@ taglib uri="/WEB-INF/tld/jesi-tags" prefix="jesi" %>
<jesi:template cache="yes">
    <c:set var="my_id" value="${param.id}"/>
    <jesi:fragment aclGroup="<%="mykey_" + pageContext.getAttribute("my_id") %>">
        <c:choose>
                <c:when test="${param.id != null }">
                    id = <c:out value="${param.id}"/>
                </c:when>
                <c:otherwise>
                    No id found
                </c:otherwise>
            </c:choose>
        </jesi:fragment>
</jesi:template>
 
 
As I understood the esi will cache the fragment for each parameter "id" I pass in the request.
However this is not what happens, the result of the first request is cached, and when I call this page with another value of the "id" parameter,
the result of the first request is returned.
 
Am I missing something here?
 
Configuration: Jahia 5.0.0 Standard edition/ Java 5 / WinXP 
 
Kind regards,
 
Nicolas