Can't partition by expression when columns are explicitly specified in the CTAS column list

create table test(x1, x2) partition by (x1) as 
select    sum(a1),  b1 
from       t1 
group by  b1;

0: jdbc:drill:schema=dfs> create table test(x1, x2) partition by (x1) as select sum(a1), b1 from t1 group by b1;
Error: SYSTEM ERROR: IllegalArgumentException: partition col x1 could not be resolved in table's column lists!
[Error Id: ab5624e8-e4dd-4752-95af-8bc2eef5d056 on atsqa4-133.qa.lab:31010] (state=,code=0)

0: jdbc:drill:schema=dfs> create table test partition by (x1) as select sum(a1) x1, b1 x2 from t1 group by b1;
+-----------+----------------------------+
| Fragment  | Number of records written  |
+-----------+----------------------------+
| 0_0       | 10                         |
+-----------+----------------------------+
1 row selected (0.904 seconds)
0: jdbc:drill:schema=dfs> select * from test;
+-------+--------+
|  x1   |   x2   |
+-------+--------+
| null  | hhhhh  |
| 2     | bbbbb  |
| 10    | jjjjj  |
| 1     | aaaaa  |
| 3     | ccccc  |
| 4     | null   |
| 5     | eeeee  |
| 7     | ggggg  |
| 6     | fffff  |
| 9     | iiiii  |
+-------+--------+
10 rows selected (0.161 seconds)
0: jdbc:drill:schema=dfs> select * from test order by x1;
+-------+--------+
|  x1   |   x2   |
+-------+--------+
| 1     | aaaaa  |
| 2     | bbbbb  |
| 3     | ccccc  |
| 4     | null   |
| 5     | eeeee  |
| 6     | fffff  |
| 7     | ggggg  |
| 9     | iiiii  |
| 10    | jjjjj  |
| null  | hhhhh  |
+-------+--------+
10 rows selected (0.299 seconds)