The opensocial spec defines proxied content as follows:
Data pipelining tags can be top level elements in the <Content> section of a gadget using Proxied Content (Section 6).
<Content href="http://example.com/canvas" xmlns:os="http://ns.opensocial.org/2008/markup">
<os:PeopleRequest key="vf" userId="@viewer" groupId="@friends"/>
When preparing a request for proxied content, a container MUST process data pipelining elements that are direct children of the proxied content's <Content> element. Data pipelining elements are ALWAYS valid when preparing a request for proxied content, even if the opensocial-data feature is not present.
However, the gadget processing of the content elements do not process the os requests or the http request and therefore nothing get posted in the request to the home server specified in the href. (Note, these may be authz=signed to support 2-legged OAuth).