mysqld crashed after performing the following steps:

on the master:

# start master mysqld with log-bin but without setting server_id
* GRANT REPLICATION SLAVE ON *.* TO "repl"@"%" IDENTIFIED BY "secret";

on the slave:

CHANGE MASTER TO MASTER_USER='repl',MASTER_PASSWORD='secret', MASTER_='192.168.23.15';
SET GLOBAL slave_parallel_threads = 2;
START SLAVE;
SHOW SLAVE STATUS\G
#  -> complains about same server_id on master and slave;
SET GLOBAL SERVER_ID=23;
STOP SLAVE; START SLAVE;
SHOW SLAVE STATUS\G
#  -> now complains about server_id not set on the master side

on the master:

SET GLOBAL SERVER_ID=42;

on the slave:

STOP SLAVE; START SLAVE;
# --> crash!

error log shows:

140512 22:07:59 [ERROR] Slave SQL: Error 'Duplicate entry '%-test-' for key 'PRIMARY'' on query. Default database: 'mysql'. Query: 'INSERT INTO db SELECT * FROM tmp_db WHERE @had_db_table=0;', Internal MariaDB error code: 1062
140512 22:07:59 [Warning] Slave: Duplicate entry '%-test-' for key 'PRIMARY' Error_code: 1062
140512 22:07:59 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'hartmut-server-bin.000001' position 63913
mysqld: /home/hartmut/projects/mariadb/releases/mariadb-10.0.10/sql/sql_base.cc:900: void close_thread_tables(THD*): Assertion `thd->transaction.stmt.is_empty() || thd->in_sub_stmt || (thd->state_flags & Open_tables_state::BACKUPS_AVAIL)' failed.
[...]
mysys/stacktrace.c:246(my_print_stacktrace)[0xdeb358]
sql/signal_handler.cc:155(handle_fatal_signal)[0x82633f]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x10340)[0x7f8bc4ed3340]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39)[0x7f8bc3cedf79]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x148)[0x7f8bc3cf1388]
/lib/x86_64-linux-gnu/libc.so.6(+0x2fe36)[0x7f8bc3ce6e36]
/lib/x86_64-linux-gnu/libc.so.6(+0x2fee2)[0x7f8bc3ce6ee2]
sql/sql_base.cc:903(close_thread_tables(THD*))[0x5d95d7]
sql/rpl_gtid.cc:689(rpl_slave_state::record_gtid(THD*, rpl_gtid const*, unsigned long long, bool, bool))[0x7afecb]
sql/rpl_gtid.cc:80(rpl_slave_state::record_and_update_gtid(THD*, rpl_group_info*))[0x7ae91c]
sql/rpl_rli.cc:1268(Relay_log_info::stmt_done(unsigned long long, long, THD*, rpl_group_info*))[0x749f24]
sql/log_event.cc:975(Log_event::do_update_pos(rpl_group_info*))[0x909159]
sql/log_event.cc:4485(Query_log_event::do_update_pos(rpl_group_info*))[0x90f573]
sql/log_event.h:1355(Log_event::update_pos(rpl_group_info*))[0x5b0f7e]
sql/slave.cc:3277(apply_event_and_update_pos(Log_event*, THD*, rpl_group_info*, rpl_parallel_thread*))[0x5a7e70]
sql/rpl_parallel.cc:46(rpt_handle_event)[0x7b3b62]
sql/rpl_parallel.cc:500(handle_rpl_parallel_thread)[0x7b4abb]
perfschema/pfs.cc:1855(pfs_spawn_thread)[0x9e893e]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x8182)[0x7f8bc4ecb182]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f8bc3db230d]