LP:619417 - the number of mysqld processes in pstree is not equal to mysqld status report

Currently, from pstree command result:

├─mysqld_safe─┬─logger
│ └─mysqld───77*[

]

But from the status of mysql:

MariaDB [(none)]> status
--------------
mysql Ver 14.16 Distrib 5.1.49-MariaDB, for debian-linux-gnu (x86_64) using readline 5.1

Connection id: 662451
Current database:
Current user: root@localhost
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server: MariaDB
Server version: 5.1.49-MariaDB-mariadb82-log (MariaDB - http://mariadb.com/)
Protocol version: 10
Connection: Localhost via UNIX socket
Server characterset: latin1
Db characterset: latin1
Client characterset: latin1
Conn. characterset: latin1
UNIX socket: /var/run/mysqld/mysqld.sock
Uptime: 5 days 23 min 34 sec

Threads: 1 Questions: 10112301 Slow queries: 14117 Opens: 3992 Flush tables: 2 Open tables: 398 Queries per second avg: 23.331

MariaDB [(none)]> SHOW STATUS LIKE 'threads%'
-> ;
------------------------+

------------------------+

------------------------+
4 rows in set (0.00 sec)

The total running threads are 55. Where is 22 threads (77-55) gone?
Please help me solve the bugs