Able to reproduce same issue with PS 5.6 wit above grammar. 

nilnandan@desktop:~/randgen$ /home/nilnandan/ps56dbg/bin/mysql -uroot -p --socket=/home/nilnandan/rqg/5.5/582358/rundir1_3/tmp/master.sock
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 17
Server version: 5.6.21-70.1-log Percona Server (GPL), Release 70.1, Revision 698

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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%thread_pool%';
+-------------------------------+--------------+
| Variable_name                 | Value        |
+-------------------------------+--------------+
| thread_pool_high_prio_mode    | transactions |
| thread_pool_high_prio_tickets | 4294967295   |
| thread_pool_idle_timeout      | 60           |
| thread_pool_max_threads       | 100000       |
| thread_pool_oversubscribe     | 3            |
| thread_pool_size              | 1            |
| thread_pool_stall_limit       | 500          |
+-------------------------------+--------------+
7 rows in set (0.00 sec)

mysql> show processlist;
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
| Id | User | Host            | db   | Command | Time | State        | Info                                                                                                 | Rows_sent | Rows_examined |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
|  1 | root | 127.0.0.1:35874 | test | Sleep   |   92 |              | NULL                                                                                                 |         0 |             0 |
| 10 | root | 127.0.0.1:35885 | test | Sleep   |    2 |              | NULL                                                                                                 |         0 |           100 |
| 11 | root | 127.0.0.1:35886 | test | Sleep   |    5 |              | NULL                                                                                                 |         0 |           505 |
| 12 | root | 127.0.0.1:35887 | test | Query   |    1 | Sending data | UPDATE LOW_PRIORITY  `table500_innodb_compressed_int` t1, `table100_innodb_default_key_pk_parts_2_in |         0 |             0 |
| 13 | root | 127.0.0.1:35888 | test | Query   |    3 | System lock  | LOAD DATA INFILE '/tmp/gentest5097.tmp' INTO TABLE `table500_innodb_dynamic_int_autoinc`             |         0 |             0 |
| 14 | root | 127.0.0.1:35889 | test | Sleep   |    2 |              | NULL                                                                                                 |         0 |         50803 |
| 17 | root | localhost       | NULL | Query   |    0 | init         | show processlist                                                                                     |         0 |             0 |
| 20 | root | 127.0.0.1:35900 | test | Sleep   |    0 |              | NULL                                                                                                 |         0 |             0 |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
8 rows in set (1.22 sec)

mysql> show processlist;
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
| Id | User | Host            | db   | Command | Time | State        | Info                                                                                                 | Rows_sent | Rows_examined |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
|  1 | root | 127.0.0.1:35874 | test | Sleep   |   97 |              | NULL                                                                                                 |         0 |             0 |
| 10 | root | 127.0.0.1:35885 | test | Sleep   |    0 |              | NULL                                                                                                 |         0 |             0 |
| 11 | root | 127.0.0.1:35886 | test | Query   |    0 | Sending data | INSERT INTO y SELECT * FROM `table100_innodb_default_key_pk_parts_2_int`                             |         0 |             0 |
| 12 | root | 127.0.0.1:35887 | test | Sleep   |    0 |              | NULL                                                                                                 |         0 |             0 |
| 13 | root | 127.0.0.1:35888 | test | Query   |    1 | System lock  | LOAD DATA INFILE '/tmp/gentest5097.tmp' INTO TABLE `table500_innodb_default_key_pk_parts_2_int_autoi |         0 |             0 |
| 14 | root | 127.0.0.1:35889 | test | Sleep   |    1 |              | NULL                                                                                                 |         0 |        201275 |
| 17 | root | localhost       | NULL | Query   |    0 | init         | show processlist                                                                                     |         0 |             0 |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
7 rows in set (0.10 sec)

mysql> show global status like '%threadpool%';
+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| Threadpool_idle_threads | 10    |
| Threadpool_threads      | 13    |
+-------------------------+-------+
2 rows in set (0.00 sec)

mysql> show processlist;

---- hang here.....