In Dutch, as in French, there's a different pronoun to use when adressing someone formally. Thing is, when calling someone 'Master' (or it's translated equivalent), the honourary term follows nearly automatically.

So to answer: No, of course there's no rule, but linguistically it would make sense and personally I do expect the honourary. And I do think it's customary, yes. Sometimes it even bugs me there's no such thing in English. (Or is there anyone here that uses forms like 'Thou' or similar?)