Last modified: 2014-09-27 09:59:50 UTC
The problem is outlined here: https://lists.wikimedia.org/pipermail/wikidata-tech/2014-September/000575.html Issue in the relevant component: https://github.com/wmde/WikibaseDataModelSerialization/issues/77
Place where a serializer maybe can be told to differentiate for json output: extensions/Wikibase.git/repo/includes/api/ApiHelperFactory.php getSerializerFactory()
https://github.com/wmde/WikibaseDataModelSerialization/pull/89