'DNS records for a zone' error codes don't match the docs

I’m currently trying to handle errors from creating/updating DNS records but it seems that the error codes listed in the docs don’t match up with what I am recieving.

For example, send an invalid MX record I get the following response:

{
    "result" : null,
    "success" : false,
    "errors" : [
      {
        "message" : "DNS Validation Error",
        "error_chain" : [
          {
            "message" : "Content for MX record must be a hostname.",
            "code" : 9009
          }
        ],
        "code" : 1004
      }
    ],
    "messages" : [

    ]
  }

According to the docs, error code 1004 would be ‘Invalid or missing zone’ and there is no mention of error code 9009. I’d probably be expecting to see 1025 ‘Invalid content for an MX record’.

Is there a reason for this difference in error codes, or are they documented somewhere I’ve not found?

Thanks