Inconsistent Wikidata query results

Question

In Wikidata, Russia is marked as both instance of "sovereign state" (Q3624078) and instance of "country" (https://www.wikidata.org/wiki/Q159).

A SPARQL request to https://query.wikidata.org/ with the "sovereign state" in its condition returns Russia:

SELECT DISTINCT ?country ?countryLabel 
WHERE
{
?country wdt:P31 wd:Q3624078 .
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
}
ORDER BY ?countryLabel

but a SPARQL request with the "country" label does not:

SELECT DISTINCT ?country ?countryLabel 
WHERE
{
?country wdt:P31 wd:Q6256 .
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
}
ORDER BY ?countryLabel

Why is to so?