Various folks did not like the fact that we disabled strict SSH host key checking to more easily enable reprovisioning related use cases. Their concerns are valid, and we should have a way to control this behavior.
In the latest 1.3, Strict checking is now on by default for both paramiko and SSH connection types.
Should you wish to disable this, you can, by either
export ANSIBLE_HOST_KEY_CHECKING=False
or in the config file
[defaults]
host_key_checking=False
I plan to cherry-pick this commit to 1.2 and cut a 1.2.1 containing only this change providing this works for everyone.