Rerender on a birt report is losing page parameters values

[bussard]

I have a jsf 2.0 xtml page with a seam birt  tag  to render a report . Everything works on the first call, but when I'm trying to rerender the report the page and EL parameters are missing .

This is my page fragment:

<h:commandButton value="Test" onclick="alert('Test Button ');">
  <a:ajax event="click" render="grf1"  />
</h:commandButton>       
<h:panelGroup id="grf1" layout="block">
  <b:birt designType="embed"
  embeddable="true"
  resourceFolder="#{request.contextPath}/reports/"
         designName="/relatorios/reportfile.rptdesign"
         masterpage="true"
  <b:param name="constantParam" value="true" />
  <b:param name="ELParam" value="#{'true'}" />
  <b:param name="pageParam" value="#{myPageParam}" />
  </b:birt>
</h:panelGroup>

I created a script to log the parmeters values in report:

java.lang.System.out.println("constantParam :"+params["constantParam"].value);
java.lang.System.out.println("ELParam :"+params["ELParam"].value);
java.lang.System.out.println("pageParam :"+params["pageParam"].value);

And this is the output at normal call:

constantParam :true
ELParam :true
pageParam :15

And this is the output at rerender call:

constantParam :true
ELParam :
pageParam :

What is the right way to rerender a birt report with parameters?