SPARQL optional limiting results

[Mikael Pesonen]

Hi, not directly related to Jena, but I have a query in which optional 
clause limits the number of results. I thought it's never possible. So 
below query returns less results with optional enabled. Wonder why is 
that and what would be the correct way to get optional data so than all 
rows are returned?

SELECT *
WHERE
{
    VALUES ?graph {<http://www.yso.fi/onto/tero/> 
<http://www.yso.fi/onto/mesh/>}
    GRAPH ?graph
    {
        {
            SELECT DISTINCT ?concept ?prefLabelm ?altLabelm WHERE
            {
                {
                    (?concept ?score1 ?prefLabelm) text:query 
(skos:prefLabel "aamiainen*") .
                    FILTER ( (lang(?prefLabelm) = "fi" ))
                }
            }
        }
   # OPTIONAL { ?concept skos:broader* [ skos:topConceptOf ?graph] }
    }
}