Steps to reproduce:

1. Set up network discovery rule, use SNMP item for uniqueness criteria
   

1. Create discovery action to create host and link template
2. See that host is created and monitored.
   
3. Because hosts get addresses from DHCP - remove interface IP address and set to use DNS:
   

Wait until hosts gets new address
Result:
New host created:

Expected:
Expected to update or add interface to existing host, because uniqueness criteria matches (same hostname), but in reality IP is still used to match hosts.