Evaluation of variables prior to SERVICE

[Sarven Capadisli]

Hi, I'm trying to understanding the way federated queries are executed 
in Fuseki/TDB [1].

My query at http://transparency.270a.info/sparql is as follows:
SELECT *
WHERE {
  ?country a dbo:Country .
  ?country owl:sameAs ?wbcountry .
  FILTER (regex(str(?wbcountry), "^http://worldbank.270a.info/";))

  SERVICE <http://worldbank.270a.info/sparql> {
      ?wbcountry skos:prefLabel ?label
  }
}

I'm expecting to get all of the labels from the WB SPARQL endpoint.

This query works fine, however, I'm puzzled about the way ?wbcountry is 
evaluated before it gets sent over SERVICE. What happens is that, FILTER 
is not applied prior to SERVICE. On the http://worldbank.270a.info/ 
server-side, I can see that all possible values of ?wbcountry are being 
matched for skos:prefLabel ?label.

My intuition tells me that, the FILTER should have prevented that by 
having ?wbcountry only evaluate to IRIs which start with 
"http://worldbank.270a.info/";. I think this is inline with 
http://www.w3.org/TR/sparql11-federated-query/#variableService - even 
though it is not an official way of evaluating.

Any feedback is appreciated.

[1] $ java tdb.tdbquery --version
Jena:       VERSION: 2.7.4-SNAPSHOT
Jena:       BUILD_DATE: 20121005-1119
ARQ:        VERSION: 2.9.4-SNAPSHOT
ARQ:        BUILD_DATE: 20121005-1119
TDB:        VERSION: 0.9.4-SNAPSHOT
TDB:        BUILD_DATE: 20121005-1119

-Sarven