ALTER TABLE proceeds despite reporting ER_TOO_LONG_KEY error

MariaDB [test]> create table t1(a TEXT not null) ROW_FORMAT=DYNAMIC;

Query OK, 0 rows affected (0.02 sec)

MariaDB [test]> create index idx1 on t1(a(3073));

ERROR 2013 (HY000): Lost connection to MySQL server during query

2017-02-04 21:32:18 140557726610176 [Note] InnoDB: Online DDL : Start applying row log

2017-02-04 21:32:18 140557726610176 [Note] InnoDB: Online DDL : End of applying row log

2017-02-04 21:32:18 140557726610176 [Note] InnoDB: Online DDL : Completed

mysqld: /home/nirbhay/project/git-repo/mariadb/10.2/sql/sql_error.cc:380: void Diagnostics_area::set_ok_status(ulonglong, ulonglong, const char*): Assertion `!is_set() || (m_status == DA_OK_BULK && is_bulk_op())' failed.

170204 21:32:18 [ERROR] mysqld got signal 6 ;

This could be because you hit a bug. It is also possible that this binary

or one of the libraries it was linked against is corrupt, improperly built,

or misconfigured. This error can also be caused by malfunctioning hardware.

To report this bug, see https://mariadb.com/kb/en/reporting-bugs

We will try our best to scrape up some info that will hopefully help

diagnose the problem, but since we have already crashed, 

something is definitely wrong and this may fail.

Server version: 10.2.4-MariaDB-debug

key_buffer_size=134217728

read_buffer_size=131072

max_used_connections=1

max_threads=153

thread_count=7

It is possible that mysqld could use up to 

key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 467287 K  bytes of memory

Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0x7fd604417070

Attempting backtrace. You can use the following information to find out

where mysqld died. If you see no messages after this, something went

terribly wrong...

stack_bottom = 0x7fd6255d6a80 thread_stack 0x48c00

./bin/mysqld(my_print_stacktrace+0x38)[0x558e471ce1cb]

addr2line: './bin/mysqld': No such file

./bin/mysqld(handle_fatal_signal+0x3a3)[0x558e46a3b896]

/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fd62390b390]

/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38)[0x7fd622cc5428]

/lib/x86_64-linux-gnu/libc.so.6(abort+0x16a)[0x7fd622cc702a]

/lib/x86_64-linux-gnu/libc.so.6(+0x2dbd7)[0x7fd622cbdbd7]

/lib/x86_64-linux-gnu/libc.so.6(+0x2dc82)[0x7fd622cbdc82]

./bin/mysqld(_ZN16Diagnostics_area13set_ok_statusEyyPKc+0x89)[0x558e467a7961]

./bin/mysqld(_Z5my_okP3THDyyPKc+0x4e)[0x558e4675cd0d]

./bin/mysqld(_Z17mysql_alter_tableP3THDPcS1_P14HA_CREATE_INFOP10TABLE_LISTP10Alter_infojP8st_orderb+0x2931)[0x558e468a5893]

./bin/mysqld(_Z21mysql_execute_commandP3THD+0x2f9a)[0x558e467d5366]

./bin/mysqld(_Z11mysql_parseP3THDPcjP12Parser_statebb+0x29d)[0x558e467e184b]

./bin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcjbb+0xf2f)[0x558e467cf6a1]

./bin/mysqld(_Z10do_commandP3THD+0x712)[0x558e467ce092]

./bin/mysqld(_Z24do_handle_one_connectionP7CONNECT+0x1ca)[0x558e469165b1]

./bin/mysqld(handle_one_connection+0x30)[0x558e46916331]

/lib/x86_64-linux-gnu/libpthread.so.0(+0x76ba)[0x7fd6239016ba]

/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7fd622d9682d]

Trying to get some variables.

Some pointers may be invalid and cause the dump to abort.

Query (0x7fd604461088): create index idx1 on t1(a(3073))

Connection ID (thread ID): 7

Status: NOT_KILLED

Optimizer switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on

The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains

information that should help you find out what is causing the crash.

Aborted (core dumped)