I dare suggest rewording completely as this is essentially a long-winded way of saying "Make sure your dns_canonicalize_hostname is true but actually try fallback and false too or ask around". Plus, there's a couple of typos and the grammar is odd overall.

Something like:

• Wrong service ticket E.g. because your instance is hidden behind a proxy.
  In such a case, you'll see a wrong principal in the output, such as e.g.
  HTTP/proxy10.fedoraproject.org@FEDORAPROJECT.ORG. Kerberos
  authentication will fail because krbV will try to fetch a service ticket for
  PTR instead of a DNS record, effectively asking for a wrong service.
  The correct form is HTTP/koji.fedoraproject.org@FEDORAPROJECT.ORG
  (also listed as "Ticket Server" in klist output). This problem is usually
  caused by a wrong value of dns_canonicalize_hostname in /etc/krb5.conf.
  Please try setting it to true, fallback and false in turn,
  as different values may be required depending on your situation.

Commit a5a2ac38 fixes this pull-request