wrong data structure serializing in turtle format

[guenterh]

@witzigs fyi

example
http://data.swissbib.ch/bibliographicResource/49783684X.turtle

look at predicate ns1:P60470

@Prefix dc: http://purl.org/dc/terms/ .
@Prefix ns0: http://data.swissbib.ch/docs.jsonld#BibliographicResource/ .
@Prefix xsd: http://www.w3.org/2001/XMLSchema# .
@Prefix dc11: http://purl.org/dc/elements/1.1/ .
@Prefix ns1: http://rdaregistry.info/Elements/u/ .
@Prefix ns2: http://www.w3.org/2000/01/rdf-schema#/ .

http://data.swissbib.ch/bibliographicResource/49783684X
a dc:BibliographicResource ;
ns0:id "49783684X"^^xsd:string ;
dc11:format "1 livre électronique"^^xsd:string ;
dc:contributor http://data.swissbib.ch/person/baa2de57-3558-3d19-97d6-c6fce4fd743e ;
dc:issued "2009-1788"^^xsd:string ;
dc:language http://lexvo.org/id/iso639-3/eng ;
dc:title "The answer of Warren Hastings : Esquire, to the articles exhibited by the knights, citizens, and burgesess [sic] in Parliament assembled, ... in maintenance of their impeachment against him for high crimes and misdemeanours ... Delivered ... Wednesday, November 28th, 1787"^^xsd:string ;
http://rdaregistry.info/Elements/u/ http://rdvocab.info/termList/RDAContentType/1020, http://rdvocab.info/termList/RDAMediaType/1003 ;
ns1:P60163 http://sws.geonames.org/2635167/ ;
ns1:P60333 <London : printed for John Murray; John Stockdale; John Sewell; W. Creech, Edinburgh; and Anthony Gerna, Dublin, 1788> ;
ns1:P60470 <{"@context":{"@vocab":"http://data.swissbib.ch/Reproduction of original from British Library> ;
ns2:idDefinedBy http://data.swissbib.ch/document/49783684X .