Problem description: in case if some host is monitored by proxy and server time is falling behind proxy time for a couple of minutes, then the item test functionality (which is described here) will not work properly, because the proxy will not process the request and will return an error message "The task has been expired."
This does not apply to cases when different timezones are used for proxy and server (item test works fine in this case).

Suggestion is to add a note ti the above mentioned documentation to make sure that server time and proxy time are synchronized (this doesn't apply to different timezones) to avoid such situations.