Currently, when create new droplets using the same Standart OS Image (e.g. Ubuntu 12.04 x64 Server), we get the nodes with the same (predefined in image) ssh host keys. Different IPs, but exactly equivalent Host Keys. But each node should have unique ssh host keys for security reasons and verification's purpose.
Suggest a generate SSH Host Keys for all new droplet on create or rebuild (from custom snapshots too) via executing (for Ubuntu): ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key (and similar for other OS).