Some name servers include partial rrsets in truncated responses, some decide it's best to omit the entire rrset, some decide it's best to omit that entire secti

Some name servers include partial rrsets in truncated responses, some decide it's best to omit the entire rrset, some decide it's best to omit that entire section. All of those behaviors are valid (RFC2181 section 9 is about as detailed as it gets). I think there's enough variety that really there's no "normal" for this.