Flush status; adds twice to global values

--pre requisites:
-- have long_query_time = 2

mysql [localhost] {msandbox} ((none)) > show global status like 'Slow_queries';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries | 0 |
+---------------+-------+
1 row in set (0.00 sec)

-- Run a query to increase 'slow_queries' counter
mysql [localhost] {msandbox} ((none)) > select sleep (2);
+-----------+
| sleep (2) |
+-----------+
| 0 |
+-----------+
1 row in set (2.00 sec)

-- check slow_queries have increased
mysql [localhost] {msandbox} ((none)) > show global status like 'Slow_queries';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries | 1 |
+---------------+-------+
1 row in set (0.00 sec)

mysql [localhost] {msandbox} ((none)) > exit
Bye
carlos.tutte@bm-support01:~/sandboxes/5.7.22$ ./use 
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.22-22 Percona Server (GPL), Release 22, Revision f62d93c

Copyright (c) 2009-2018 Percona LLC and/or its affiliates
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

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

mysql [localhost] {msandbox} ((none)) > show global status like 'Slow_queries';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries | 1 |
+---------------+-------+
1 row in set (0.00 sec)

mysql [localhost] {msandbox} ((none)) > select * from performance_schema.status_by_user where variable_name in ('Slow_queries');
+----------+---------------+----------------+
| USER | VARIABLE_NAME | VARIABLE_VALUE |
+----------+---------------+----------------+
| NULL | Slow_queries | 0 |
| msandbox | Slow_queries | 1 |
+----------+---------------+----------------+
2 rows in set (0.00 sec)

mysql [localhost] {msandbox} ((none)) > flush status;
Query OK, 0 rows affected (0.00 sec)

mysql [localhost] {msandbox} ((none)) > select * from performance_schema.status_by_user where variable_name in ('Slow_queries');
+----------+---------------+----------------+
| USER | VARIABLE_NAME | VARIABLE_VALUE |
+----------+---------------+----------------+
| NULL | Slow_queries | 0 |
| msandbox | Slow_queries | 0 |
+----------+---------------+----------------+
2 rows in set (0.00 sec)

-- slow_queries have increased twice
mysql [localhost] {msandbox} ((none)) > show global status like 'Slow_queries';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries | 2 |
+---------------+-------+
1 row in set (0.00 sec)