rocksdb: crash & corruption, charsets, indexed cols

Version: '5.7.20-19' (Built on 09 January 2018 with gcc (GCC) 8.0.0 20180101 (experimental))
2018-01-09T15:46:56.677401Z 3 [Note] CHECKTABLE t: Checking table t
 2018-01-09T15:46:56.677427Z 3 [Note] CHECKTABLE t: Checking index h
 2018-01-09T15:46:56.677499Z 3 [Note] CHECKTABLE t: ... 1 index entries checked (0 had checksums)
 2018-01-09T15:46:56.677517Z 3 [Note] CHECKTABLE t: 0 table records had checksums
 2018-01-09T15:46:56.686764Z 3 [Note] CHECKTABLE t: Checking table t
 2018-01-09T15:46:56.686786Z 3 [Note] CHECKTABLE t: Checking index h
Program received signal SIGSEGV, Segmentation fault.
 myrocks::Rdb_key_def::unpack_record at /usr/include/bits/string3.h:51
 51 return _builtin_memcpy_chk (dest, __src, __len, __bos0 (_dest));
 (gdb) bt
 #0 in myrocks::Rdb_key_def::unpack_record at /usr/include/bits/string3.h:51
 #1 in myrocks::ha_rocksdb::secondary_index_read at ./storage/rocksdb/ha_rocksdb.cc:6735
 #2 in myrocks::ha_rocksdb::index_next_with_direction at ./storage/rocksdb/ha_rocksdb.cc:7438
 #3 in myrocks::ha_rocksdb::index_first_intern at ./storage/rocksdb/ha_rocksdb.cc:7550
 #4 in myrocks::ha_rocksdb::index_first at ./storage/rocksdb/ha_rocksdb.cc:7457
 #5 in myrocks::ha_rocksdb::check () at ./storage/rocksdb/ha_rocksdb.cc:7125
 #6 in handler::ha_check at ./sql/handler.cc:4829
 #7 in mysql_admin_table () at ./sql/sql_admin.cc:708
 #8 in Sql_cmd_check_table::execute at ./sql/sql_admin.cc:1227
 #9 in mysql_execute_command () at ./sql/sql_parse.cc:5121
 #10 in mysql_parse at ./sql/sql_parse.cc:5897
 #11 in dispatch_command () at ./sql/sql_parse.cc:1493
 #12 in do_command at ./sql/sql_parse.cc:1021
 #13 in handle_connection at ./sql/conn_handler/connection_handler_per_thread.cc:312
 #14 in pfs_spawn_thread at ./storage/perfschema/pfs.cc:2190
 #15 in start_thread at pthread_create.c:308

set sql_mode ='';
drop table if exists t;
create table t (
  h varchar(31) character set utf8 collate utf8_bin not null,
  i varchar(19) collate latin1_bin not null,
  primary key(i),
  key(h)
) engine=rocksdb;
insert into t(i,h) values('a','b');
check table t;
alter table t modify h varchar(31) character set cp1257 collate cp1257_bin not null;
check table t;