[Trinidad] PPR - getting full page refresh instead of partial refresh

[noah]

Maybe I just don't understand how PPR is supposed to work.

I have this page (Facelets, 1.2-07-apr-SNAPSHOT, 1.2 RI, FF 2):
<tr:document xmlns="http://www.w3.org/1999/xhtml";
  xmlns:ui="http://java.sun.com/jsf/facelets";
  xmlns:f="http://java.sun.com/jsf/core";
  xmlns:c="http://java.sun.com/jstl/core";
  xmlns:tr="http://myfaces.apache.org/trinidad";
  xmlns:h="http://java.sun.com/jsf/html"; title="Trinidad Test">
  <tr:form >

     <tr:panelBox background="transparent" partialTriggers="preview">
        <h:outputText escape="false" value="#{pageFlowScope.text}" />
     </tr:panelBox>

     <tr:inputText value="#{pageFlowScope.text}" columns="100" rows="25"/>

     <tr:commandButton id="preview" partialSubmit="true" text="Preview" />

     Text='#{pageFlowScope.text}'

  </tr:form>
</tr:document>

Now I get the expected rendering.  I get Text='' (i.e. no update) and
the panelBox is updated, but it's happening as a normal POST with full
page refresh.  Have I done something wrong or is this the expected
behavior?