Query over multiple named graphs

Support
1

I have a problem when performing a query over multiple named graphs. For instance the following works as all triples are in the HVAC-I graph:

PREFIX seas: <https://w3id.org/seas/>
PREFIX prov: <http://www.w3.org/ns/prov#>
SELECT *
FROM NAMED <https://localhost/seas/HVAC>
FROM NAMED <https://localhost/seas/HVAC-I>
WHERE {
  GRAPH ?g {
    <propURI> seas:evaluation ?eval .
    ?eval seas:evaluatedValue ?latestVal ;
          prov:wasGeneratedAtTime ?latestTime .
    OPTIONAL {
      ?eval prov:wasDerivedFrom ?depEval .
    }
  }
}

But when I extend the OPTIONAL statement with the following, I get no results (as these triples are in the HVAC graph):

OPTIONAL {
  ?eval prov:wasDerivedFrom ?depEval .
  ?depEval ^seas:evaluation ?depProp .
}

Performing the query alone does return a result:

SELECT * 
FROM NAMED <https://localhost/seas/HVAC>
WHERE { 
  GRAPH ?g { 
  	<evalURI> ^seas:evaluation ?prop
  }
}

I might have misunderstood the SPARQL syntax, but I believe what I am trying to achieve is not impossible?