LOCK TABLES FOR BACKUP should be incompatible with LOCK TABLES, FLUSH TABLES ... WITH READ LOCK, FLUSH TABLES ... FOR EXPORT in the same connection

========================= Error log:
mysqld: /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/lock.cc:1140: void Global_backup_lock::re
lease(THD*): Assertion `m_lock != __null && thd->mdl_context.is_lock_owner(m_namespace, "", "", MDL_SHARED)' failed.
13:16:55 UTC - mysqld got signal 6 ;
---
--
Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (7f55d9cd6010): UNLOCK TABLES
Connection ID (thread ID): 19
Status: NOT_KILLED

========================= gdb :
Thread 1 (LWP 14549):
+bt
#0 0x00007f56441b9771 in pthread_kill () from /lib64/libpthread.so.0
#1 0x0000000000aaa60e in my_write_core (sig=6) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/mysys/stacktrace.c:422
#2 0x0000000000727d92 in handle_fatal_signal (sig=6) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/signal_handler.cc:254
#3 <signal handler called>
#4 0x00007f5642dbd989 in raise () from /lib64/libc.so.6
#5 0x00007f5642dbf098 in abort () from /lib64/libc.so.6
#6 0x00007f5642db68f6 in __assert_fail_base () from /lib64/libc.so.6
#7 0x00007f5642db69a2 in __assert_fail () from /lib64/libc.so.6
#8 0x000000000094e244 in Global_backup_lock::release (this=0x7f560dbf0a08, thd=0x7f560dbef000) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/lock.cc:1138
#9 0x00000000007dde4f in mysql_execute_command (thd=0x7f560dbef000) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/sql_parse.cc:4168
#10 0x00000000007e4c87 in mysql_parse (thd=0x7f560dbef000, rawbuf=0x7f55d9cd6010 "UNLOCK TABLES", length=13, parser_state=0x7f564476ed10) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/sql_parse.cc:6746
#11 0x00000000007d7222 in dispatch_command (command=COM_QUERY, thd=0x7f560dbef000, packet=0x7f560dbf3001 "UNLOCK TABLES", packet_length=13) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/sql_parse.cc:1434
#12 0x00000000007d614e in do_command (thd=0x7f560dbef000) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/sql_parse.cc:1051
#13 0x00000000008b9ca7 in threadpool_process_request (thd=0x7f560dbef000) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/threadpool_common.cc:319
#14 0x00000000008bc589 in handle_event (connection=0x7f560d725b20) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/threadpool_unix.cc:1550
#15 0x00000000008bc7b9 in worker_main (param=0x1880c00 <all_groups+2048>) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/sql/threadpool_unix.cc:1603
#16 0x0000000000db42e0 in pfs_spawn_thread (arg=0x7f56263bc1a0) at /mnt/workspace/percona-server-5.6-binaries-debug-yassl/label_exp/centos6-64/percona-server-5.6.19-67.0/storage/perfschema/pfs.cc:1860
#17 0x00007f56441b4df3 in start_thread () from /lib64/libpthread.so.0
#18 0x00007f5642e7e3dd in clone () from /lib64/libc.so.6
(gdb) +set logging off

========================= Testcase reduction info:
PS startup cmd:

/ssd/ramesh/ps56dbg/bin/mysqld --basedir=/ssd/ramesh/ps56dbg --datadir=/ssd/1408675866/data --port=39460 --pid-file=/ssd/1408675866/pid.pid --log-error=/ssd/1408675866/error.log.out --socket=/ssd/1408675866/socket.sock --user=ramesh --log-output=none --sql_mode=ONLY_FULL_GROUP_BY --event-scheduler=ON > /ssd/1408675866/mysqld.out 2>&1 &

SQL_out

DROP DATABASE test;CREATE DATABASE test;USE test;
CREATE TABLE t1(
c1 CHAR(1),
key(c1)) ENGINE=innodb ROW_FORMAT=dynamic;
LOCK TABLES FOR BACKUP;
LOCK TABLE t1 READ LOCAL;
UNLOCK TABLES;