Incorrect handling of SPARQL VALUES clause

[mdesalvo]

The following query:

SELECT ?X ?Y ?N
WHERE {
  {
    {
      ?Y <ex:dogOf> ?X .
      OPTIONAL { ?X <ex:hasName> ?N } .
    }
    MINUS
    {
      {
        SELECT *
        WHERE {
          {
            ?Y <ex:dogOf> ?X .
            ?X <ex:hasColor> ?C .
          }
        }
      }
      UNION
      {
        VALUES (?Y ?X) {
          ( <ex:balto> <ex:whoever> )
        } .
      }
    }
  }
}
ORDER BY ASC(?X)

on the following datatset:

<ex:pluto> <ex:dogOf> <ex:topolino> .
<ex:topolino> <ex:hasName> "Mickey Mouse"@EN-US .
<ex:fido> <ex:dogOf> <ex:paperino> .
<ex:paperino> <ex:hasName> "Donald Duck"@EN-US .
<ex:balto> <ex:dogOf> <ex:whoever> .
<ex:baubau> <ex:dogOf> <ex:paperoga> .
<ex:paperoga> <ex:hasColor> "white" .
<ex:snoopie> <ex:dogOf> <ex:linus> .

produces 0 results, instead it should produce 3 results.
The reason is probably that we propagate the VALUES clause up to the mother query, but this clause has no a direct mother query since it lives inside a UNION/MINUS pattern group.