ALTER TABLE does not work from client

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Server version: 10.2.0-MariaDB-debug Source distribution

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MariaDB [test]> DROP TABLE IF EXISTS t1;

Query OK, 0 rows affected (0.06 sec)

MariaDB [test]> CREATE TABLE t1 (a INT, b CHAR(8)) ENGINE=InnoDB;

Query OK, 0 rows affected (0.02 sec)

MariaDB [test]> INSERT INTO t1 (a,b) VALUES (1,'a'),(2,'b'),(3,'c');

Query OK, 3 rows affected (0.00 sec)

Records: 3  Duplicates: 0  Warnings: 0

MariaDB [test]> ALTER TABLE t1 MODIFY b CHAR(16);

ERROR 65535 (HY000): 

MariaDB [test]> 

commit d4b3a199acb0ddcdedff441ae664b0a2cf2fe8d2

Author: Oleksandr Byelkin <sanja@mariadb.com>

Date:   Sun Jan 17 21:21:39 2016 +0100

    MDEV-9117: Client Server capability negotiation for MariaDB specific functionality

    New capability flags space.

    Removed old progress flag, added new one.