The Graph Literal section says the following
Concrete syntaxes MAY support simple literals, consisting of only a lexical form without any datatype IRI or language tag. Simple literals only exist in concrete syntaxes, and are treated as syntactic sugar for abstract syntax literals with the datatype IRI http://www.w3.org/2001/XMLSchema#string.
In practice, it appears that both Jena and Sesame are broken in their handling of RDF Literals. They also break graph isomorphism for the same reasons.