When adding a BMH with 

spec:
  online: true
  customDeploy:
    method: install_coreos

after inspection the BMO will provision the node in ironic 

but the node is now being created without any userdata/ignition data, 
IPA ironic_coreos_install then goes down a seldom used path to create ignition from scratch, the created ignition is invalid and the node fails to boot after it is provisioned.

Boot stalls with a ignition error "invalid config version (couldn't parse)"