Your PowerDNS ancestry shows: missing dots. ;-)
Without the trailing dot, `named-checkzone` says:
```
SOA record not at top of zone (ietf.org.ietf.org)
```
RFC 973 enumerates the changes between RFC 882/882 and RFC 1034/1035. There are several compatibility breaks:
* TTLs and serial numbers expanded from 16 bits to 32 bits: this breaks wire format compatibility;
* wildcard semantics change: an 882/883 implementation will handle them incorrectly;
* master file syntax changes: modern master files will be read incorrectly by an 882/883 parser
* CNAME semantics change: modern DNS data is probably compatible with 882/883 semantics but not the other way round;
