Wow, that's really unclear from the documentation.  Thanks for the 
report.  I have filed a pull request to fix it here: https://github.com/krb5/krb5/pull/183

(For bookkeeping, note that this ticket and #7925 both pertain to 
functionality added in #7882, which is new functionality for release 
1.13.  So it isn't a change relative to 1.12.x.)