Scalar result of subquery changes after adding an outer select stmt

mysql> create table t1(c1 int, c2 int, primary key(c2));

Query OK, 0 rows affected (0.01 sec)

mysql> insert into t1 values(2,1),(1,2);

(select c1 frQuery OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

mysql> select (select c1 from t1 group by c1,c2 order by c1 limit 1) as x;

+------+

| x    |

+------+

|    2 |

+------+

1 row in set (0.00 sec)

mysql> (select c1 from t1 group by c1,c2 order by c1 limit 1);

+------+

| c1   |

+------+

|    1 |

+------+

1 row in set (0.00 sec)

mysql> select version();

+---------------------+

| version()           |

+---------------------+

| 10.1.10-MariaDB-log |

+---------------------+

1 row in set (0.00 sec)

drop table t1;

create table t1(c1 int, c2 int, primary key(c2));

insert into t1 values(2,1),(1,2);

select (select c1 from t1 group by c1,c2 order by c1 limit 1) as x;

(select c1 from t1 group by c1,c2 order by c1 limit 1);