This query

PREFIX bd: <http://www.bigdata.com/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>
PREFIX wikibase: <http://wikiba.se/ontology#>
SELECT ?q ?qLabel ?tag WHERE {
	?q <http://www.wikidata.org/prop/direct/P1482> ?tag .
	SERVICE wikibase:label {
		bd:serviceParam wikibase:language "en" .
	}
}

results in an error unless you omit PREFIX bd: <http://www.bigdata.com/>. Without this prefix definition, however, the query is no valid SPARQL (although blazegraph does not care). I guess the namespace http://www.bigdata.com/ is wrong?

P.S: The same applies to namespace hint: used in hint:Query hint:optimizer "None" .