@itemref functionality wrt itemtype context

Today during the call Ivan raised a concern about @itemref when it is used
to associate several items to the same set of properties. His concern was
that these properties would possibly inherit different @itemtype contexts.

Here is a first snippet describing a movie and an article using different
vocabularies:

<div itemscope itemtype="http://schema.org/Movie" itemref="license">
<p itemprop="name">Pirates of the Carribean: On Stranger Tides (2011)</p>
</div>
<div itemscope itemtype="http://rdfs.org/sioc/ns#Post" itemref="license">
  <span itemprop="name">How to Tie a Reef Knot</span>
  by <span itemprop="author">John Doe</span>
</div>
<footer>
 <p id="license">All content licensed under the <a itemprop="license"
 href="http://www.opensource.org/licenses/mit-license.php">MIT
 license</a>.</p>
</footer>

Even though there is no official RDF conversion for microdata yet, I used
Gregg's RDF distiller [1] to convert to RDF. The following property URIs
were generated for the @itemprop license token:
http://rdfs.org/sioc/ns#license
http://schema.org/license

Another example:

<div>
  <div itemscope itemtype="http://xmlns.com/foaf/0.1/Person"
itemref="a"></div>
  <div itemscope itemtype="http://schema.org/Person" itemref="a"></div>
  <p id="a">Name: <span itemprop="name">Amanda</span></p>
</div>

which yields:
http://xmlns.com/foaf/0.1/name
http://schema.org/name

Microdata does not care much about full URIs for properties, and uses the
tokens as is in the JSON output (I guess it's up to the application
consuming the data to check if a given property name makes sense in the
context of its type, but I guess most won't check that). This can be
cumbersome for the conversion to RDF where a namespace is required to build
a proper URI for the property. Here's another use case which I didn't
include in the example above: @itemtype is optional in microdata, so if it
is omitted, there is no source to infer a namespace from during the
conversion to RDF.

@Ivan, does that illustrate all of your points re @itemref?

Steph.