Steps to reproduce:

1. Resolve warning message manually.
2. Check if the problem has been resolved
3. Check dashboard 'host status' if it still shows the warning message.
4. The warning sign is still seen there when Monitoring -> Problems says there is no data. 

The warning message occured by SNMPv2 trigger, it was triggered to show 'No data collection' when there is no answer(Ack) from the device longer than 3 minutes collected form SNMP agent. 

I also had the recovery expression to this but it seems the OK message didn't work.

The device connected to Zabbix through SNMP was Cisco Firewall(Network device ), the same SNMP problem occured about 5 times over weeks but only SNMP problem with this bug is the problem occured on a specific date. The other problems which are the same but occured on different dates all cleared away after they were manually resolved