[CentOS] ssh keys hostname VS fqdn - offends?

Hi guys

Though being a mere user, - as opposed to an expert - in many long years of ssh in my use this, is new:

-> $ ssh box5.proxmox.mine hostname -i 10.3.1.78

-> $ ssh box5 hostname -i Warning: the RSA host key for 'box5' differs from the key for the IP address '10.3.1.78' Offending key for IP in /root/.ssh/known_hosts:2 Matching host key in /etc/ssh/ssh_known_hosts:2 Are you sure you want to continue connecting (yes/no)? yes 10.3.1.78

This is same one host I _ssh_ to. Is this purely _ssh_ and way to fix it would be 'configuration' or perhaps (ssh &) something else? I don't quite get what exactly is happening here.

many thanks, L.