Assertion `0' failed on creating a unique index on a Mroonga table with non-unique values

mysqld: 10.0/sql/protocol.cc:522: void Protocol::end_statement(): Assertion `0' failed.

141005  2:07:44 [ERROR] mysqld got signal 6 ;

#6  0x00007f43b969b6f1 in *__GI___assert_fail (assertion=0xef70d0 "0", file=<optimized out>, line=522, function=0xef85e0 "void Protocol::end_statement()") at assert.c:81

#7  0x00000000005d2bab in Protocol::end_statement (this=0x7f43a0f175f8) at 10.0/sql/protocol.cc:522

#8  0x0000000000679aba in dispatch_command (command=COM_QUERY, thd=0x7f43a0f17070, packet=0x7f43a0e18071 "alter table t1 add unique index (a)", packet_length=35) at 10.0/sql/sql_parse.cc:1728

#9  0x0000000000677a31 in do_command (thd=0x7f43a0f17070) at 10.0/sql/sql_parse.cc:1004

#10 0x00000000007942a6 in do_handle_one_connection (thd_arg=0x7f43a0f17070) at 10.0/sql/sql_connect.cc:1379

#11 0x0000000000793ff9 in handle_one_connection (arg=0x7f43a0f17070) at 10.0/sql/sql_connect.cc:1293

#12 0x00007f43bb254b50 in start_thread (arg=<optimized out>) at pthread_create.c:304

#13 0x00007f43b974c20d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112

# For MTR, replace it with however Mroonga should be properly initialized there

source ./storage/mroonga/data/install.sql;

create table t1 (a int) engine=Mroonga;

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

alter table t1 add unique index (a);