If a previously created A record is deleted via the API, recreating a new one always produces a "Duplicate host record" when trying to recreate the record. I have verified that the record does not exist by listing all the A records first, before issuing the POST.
As far as I can tell, there there is no update option (even if you specify the RecordId during the POST), so I thought it would be best to first delete all the records, then add all the updated records from the DNS Management form. Despite the error, the records still get created.
I posted an earlier Issue that relates to this but for some reason my issue was removed. I would appreciate knowing why.