My mistake, I should have linked to https://www.wikidata.org/wiki/Property_talk:P1647, which includes the following in the 'Examples' section of the documentation template:

"Note: it is not valid to declare subproperties of instance of (P31) (rdf:type), subclass of (P279) (rdfs:subClassOf) or any other property mapped to a built-in property of RDF, RDFS or OWL. See creation discussion."