lp:1010729 Unexpected syntax error for a query with UNION of left joins

CREATE TABLE t1 (a int);

CREATE TABLE t2 (b int);

CREATE TABLE t3 (c int);

SELECT a FROM t1 UNION SELECT b FROM t2 JOIN (t3) ON ( t2.b = t3.c );

MariaDB [test]> SELECT a FROM t1 UNION SELECT b FROM t2 JOIN (t3) ON ( t2.b = t3.c );

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ON ( t2.b = t3.c )' at line 1

MariaDB [test]> SELECT b FROM t2 JOIN (t3) ON ( t2.b = t3.c ) UNION SELECT a FROM t1;

Empty set (0.00 sec)