A host is normally created with a Kerberos principal set except in the case where it is created with either a user-provided or random password for OTP enrollment.

If you create a host with a NULL password, --password=, the principal is not set and the Kerberos objectclasses aren't added. No password is actually set on the host.

I think the issue is in the pre callback in this line:

if 'userpassword' not in entry_attrs and not options.get('random', False):
# create the principal, append the objectclasses

To reproduce compare the output of the first to the second:

$ ipa host-add --all --raw somehost
$ ipa host-add --all --raw --password= someotherhost