Comment 8 for bug 2012801

> It's perfectly valid for there to be more than one PTR record for any given IP

It may not be a clear violation of RFCs indeed, but it can confuse software by having multiple PTR records (and somehow MAAS 3.3 has multiple PTR records for some of them not all).
https://serverfault.com/questions/618700/why-multiple-ptr-records-in-dns-is-not-recommended

Even if we leave charms out of the picture, MAAS 2.2's behavior is somewhat "preferred" to be the single source of truth of a data center with its IPAM functionality.