Prepared statement with parameters in new DEFAULT syntax fails with syntax error upon execution

MariaDB [test]> set @a=1, @b=2;

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> prepare stmt from "create or replace table t1 (i int default (?+?))";

Query OK, 0 rows affected (0.00 sec)

Statement prepared

MariaDB [test]> execute stmt using @a,@b;

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 '?+?)' at line 1

MariaDB [test]> prepare stmt from "create or replace table t1 (i int default (?))";

Query OK, 0 rows affected (0.00 sec)

Statement prepared

MariaDB [test]> execute stmt using @a;

Query OK, 0 rows affected (0.65 sec)