The result of UNIQUEJOIN on Hive on Tez is inconsistent with that of MR

The result of UNIQUEJOIN on Hive on Tez is inconsistent with that of MR, and the result Is not correct, for example:

CREATE TABLE T1_n1x(key STRING, val STRING) STORED AS orc;
CREATE TABLE T2_n1x(key STRING, val STRING) STORED AS orc;

insert into T1_n1x values('aaa', '111'),('bbb', '222'),('ccc', '333');
insert into T2_n1x values('aaa', '111'),('ddd', '444'),('ccc', '333');

SELECT a.key, b.key FROM UNIQUEJOIN PRESERVE T1_n1x a (a.key), PRESERVE  T2_n1x b (b.key);

Hive on Tez result: wrong

------------------
Hive on MR result: right

-----------------

SELECT a.key, b.key FROM UNIQUEJOIN T1_n1x a (a.key), T2_n1x b (b.key);

Hive on Tez result: wrong

-------------------

-----------------

Hive on MR result: right