Partition pruning information not available in query plan for COUNT aggregate query

0: jdbc:drill:schema=dfs.tmp> CREATE TABLE tbl_prtn_prune_01 PARTITION BY (col_state) 
AS 
SELECT CAST(columns[0] AS DATE) col_date, 
CAST(columns[1] AS CHAR(3)) col_state, 
CAST(columns[2] AS INTEGER) col_prime, 
CAST(columns[3] AS VARCHAR(256)) col_varstr, 
CAST(columns[4] AS INTEGER) col_id, 
CAST(columns[5] AS VARCHAR(50)) col_name 
from `partition_prune_data.csv`;
+-----------+----------------------------+
| Fragment  | Number of records written  |
+-----------+----------------------------+
| 0_0       | 1638640                    |
+-----------+----------------------------+
1 row selected (17.675 seconds)

0: jdbc:drill:schema=dfs.tmp> select COUNT(*) from tbl_prtn_prune_01 where col_state = 'CA';
+---------+
| EXPR$0  |
+---------+
| 35653   |
+---------+
1 row selected (0.471 seconds)

0: jdbc:drill:schema=dfs.tmp> explain plan for select COUNT(*) from tbl_prtn_prune_01 where col_state = 'CA';
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(EXPR$0=[$0])
00-02        Project(EXPR$0=[$0])
00-03          Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@1d4bb67d[columns = null, isStarQuery = false, isSkipQuery = false]])

0: jdbc:drill:schema=dfs.tmp> refresh table metadata tbl_prtn_prune_01;
+-------+-------------------------------------------------------------+
|  ok   |                           summary                           |
+-------+-------------------------------------------------------------+
| true  | Successfully updated metadata for table tbl_prtn_prune_01.  |
+-------+-------------------------------------------------------------+
1 row selected (0.321 seconds)

0: jdbc:drill:schema=dfs.tmp> explain plan for select COUNT(col_state) from tbl_prtn_prune_01 where col_state = 'CA';
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(EXPR$0=[$0])
00-02        Project(EXPR$0=[$0])
00-03          Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@2e0f4be9[columns = null, isStarQuery = false, isSkipQuery = false]])

0: jdbc:drill:schema=dfs.tmp> explain plan for select COUNT(*) from tbl_prtn_prune_01 where col_state = 'CA';
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(EXPR$0=[$0])
00-02        Project(EXPR$0=[$0])
00-03          Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@3fc1f8e7[columns = null, isStarQuery = false, isSkipQuery = false]])

0: jdbc:drill:schema=dfs.tmp> explain plan for select COUNT(col_date) from tbl_prtn_prune_01 where col_state = 'CA';
+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(EXPR$0=[$0])
00-02        Project(EXPR$0=[$0])
00-03          Scan(groupscan=[org.apache.drill.exec.store.pojo.PojoRecordReader@7afc851e[columns = null, isStarQuery = false, isSkipQuery = false]])