Property chain axioms and cyclic dependencies

Hello,

I'm trying to understand in which cases it's allowed to use
owl:propertyChainAxiom and when it's not.

I've written a small ontology to understand it (I pasted it at the end),
but I still couldn't figure out why HermiT (using Protege) says "The given
property hierarchy is not regular" and "There is a cyclic dependency
involving property :isRelative".

I know there's a loop there but what is the real problem? After all, how is
that different from a owl:TransitiveProperty? Any way to intuitively
understand what is wrong with it?

Any idea?

Thank you,
Matt

---
@prefix : <http://foo/bar#>.
@prefix owl: <http://www.w3.org/2002/07/owl#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.

:Person a owl:Class.

:isRelativeOf
  a owl:TransitiveProperty;
  rdfs:domain :Person;
  rdfs:range :Person;
..

  :isAncestorOf
    rdfs:subPropertyOf :isRelativeOf;
    owl:propertyChainAxiom (:isRelativeOf :isAncestorOf);
  .
---