UNION ALL with ORDER BY fails when column aliases don't match

SELECT x
FROM
(SELECT Sum(ss_ext_sales_price) x
FROM  store_sales
UNION ALL
SELECT Sum(cs_ext_sales_price) y
FROM catalog_sales) tmp
ORDER BY x;

SELECT x
FROM
(SELECT ss_ext_sales_price x
FROM  store_sales
UNION ALL
SELECT cs_ext_sales_price y
FROM catalog_sales) tmp
ORDER BY x;

SELECT x
FROM
(SELECT ss_ext_sales_price x
FROM  store_sales
UNION ALL
SELECT ss_ext_sales_price y
FROM store_sales) tmp
ORDER BY x;

Error from Drill:
Query failed: RemoteRpcException: Failure while running fragment., Sort doesn't currently support sorts with changing schemas. 
java.lang.RuntimeException: java.sql.SQLException: Failure while executing query.
...