Nick narrowed this down. This is caused by a bug in reporting the primary key columns of the query. Really there isn't a primery key but the store thinks there is and all the records get written on top of each other. I need to investigate further, but I believe there is a simple work around. If you select datasetid I believe everything will work.

So try either

SELECT * FROM study.DataSets ...

or

SELECT Name, DataSetId FROM study.DataSets ...