Just wanted to note this, for anyone else struggling.
Fuseki 1.0.x used to return a proprietary JSON format for RDF when running DESCRIBE or CONSTRUCT queries. After switching to Fuseki 1.1.2 it defaults to JSON-LD.
If you want to upgrade, without making all your applications handle JSON-LD, then use “json-rdf” as the output format.
The offending code in github: