The variantmap data is (if memory serves) unmodified from the JSON blob returned for the request.  As such, the field names won't always match what the user expects (eg, we use camel-casing instead of underscores, in multi-word field names).

This might prove surprising to clients, since they will expect the QML api field names to work.
I think we should convert the given (QML-conforming) field name into a Facebook api field name, via ontology lookup.  We certainly need to document the semantics of this field property, giving a few examples (eg of fields which are camelcased properties in the QML api, etc.