tab completion fails between prefix and local name

[joshsh]

Having typed a namespace prefix, followed by a colon, pressing 'Tab' should reveal all known terms in the namespace. That no longer happens.

1 >>  rdf:type.

rdf:_1  (rdf:type)
   rdf:type
      rdf:Property;
   rdfs:isDefinedBy
      rdf:;
   rdfs:label
      "type";
   rdfs:comment
      "The subject is an instance of a class.";
   rdfs:range
      rdfs:Class;
   rdfs:domain
      rdfs:Resource.

2 >>  rdf: