Steps to reproduce:

1. Use default configuration file /etc/zabbix/zabbix_agent2.conf with modified content:

   Server=myserver.example.test
   ServerActive=myserver.example.test
   Hostname=myclient.example.test
   DebugLevel=5

   1. CUSTOM USERPARAMETER
      UserParameter=test.sleep8,/usr/bin/sleep 8000 && echo "ok"
      UserParameter=test.sleep9,/usr/bin/sleep 9000 && echo "ok"

2. Add an active item on zabbix server with parameters:
   Key: test.sleep8
   Update interval: 1m
   Timeout: 15s (or whatever low enough)
3. Add another passive item on zabbix server with parameters:
   Key: test.sleep9
   Update interval: 1m
   Timeout: 15s (or whatever low enough)
   Other parameters do not matter, see screenshot attached.
4. Run agent and wait for some time.

Result:
After some time, both items become unsupported due to timeout. But child processes "/usr/bin/sleep" are duplicated and not killed (both active and passive checks).

root@myclient ~ [#] pgrep sleep | wc -l
12

Agent log looks fine, timeouts are reported in log.

**

Expected:
Expected result: 0 child processes, 0 leftovers.
After timeout, all child userparameter processes should be killed by force.
Everything works fine on old agent2 version 6.*