Could you try a couple of things to try to help pinpoint the source of the problem?
1. Can you run an explain of that query and paste the results here?
explain select * from part_test_date where first_date between ‘2014-10-01′ and ‘2014-10-15′;
That would let us know if vectorization is being used, and whether there is a problem there.
2. The table is using ORC storage. If you create a table with something other than ORC (say STORED AS TEXTFILE), do you get the same problem, or do the query results come out as expected?