When a poller performs the ping and the snmp ping at the start of a poll, it will assume the device is UP if the results are ok.
But if the device stops responding after that point, then this happens:
I had a chat on IRC about this:
<Gunni> adama: why does this happen?
<Gunni> can your poller not notice the request timed out, vs the value being set to ''?
<landy> that happen when device down after check their status, mean ping and snmp ping return ok, but after stop responding
<landy> try increase snmp timeout
<Gunni> yeah i expected that landy, but can't the script notice that and ... abandon the poll or some instead of clearing all fields?
<landy> check status before each module - derp idea