Steps to reproduce:
1) Create item with type - Zabbix trapper.
2) Open created items and change Type to - HTTP agent.
(fill URL with any link).
3) Press "Test" button.
4) In appeared form press - "Get value and test"

Result:
Error message - Unsupported timeout value.

Expected:
No error message.
to make error message disappear, we need select timeout - Override and then to back to Global.