When a ReflectDatumReader is used to read implementations of SpecificRecord, it fails if the SpecificRecord includes an (avro) array. This appears to be due to the fact that the newArray method in ReflectDatumReader works differently (based on a reflection-based schema) than the newArray method in GenericDatumReader (which is the base class of the DatumReaders).
The included patch simply removes the delegation to SpecificData for the creation of a schema in the case of a SpecificRecord. My assumption is that the delegation to SpecificData is for performance reasons.
The rationale in removing the delegation to SpecificData is that a) it doesn't work completely correctly, as demonstrated, and b) if a user is using ReflectDatumReader (instead of SpecificDatumReader) to read SpecificRecords, there may be other underlying reasons that reflection is specifically chosen, and so this intention should not be undermined by the delegation to SpecificData.