In MEX PutMetadata it says:

----
[Body]/mex:PutMetadata/mex:Metadata
...
    If a MetadataSection child contains a MetadataReference or MetadataLocation instead of the metadata in-lined, the endpoint MAY reject the PutMetadata request with an mex:UnsupportedMetadata fault. 
----

The spec is clear on what to do if the service doesn't like the references,
and to me, this implies that if it does like the references it will place use
those references when someone asks for the metadata.  In other words, 
the service is not supposed to follow those refs, grab the data so that it
can return the metadata inlined in a future getMetadata request. Instead it
should return these refs.  However, this isn't spelled out - as it current
stands someone might interpret the spec to imply that the service is supposed
to follow those refs.

High Level Proposal:
Add text clarifying that a service is not to follow the refs, rather
treat this PutMetadata operation as a way to update the references the
service is storing.