CAA (or Certification Authority Authorization) records are a fairly new type, intended for enhanced security.
We do support CAA records, but for the time being we need to add them for you. Please login to your iwantmyname account and send us an authenticated request via our support form including the required CAA record syntax:
Syntax: <flags> <tag> <value>
E.g. 128 issue "mydomain.com"
Once we have that information we can make the update for you and provide additional information to check once the setup is propagated and working. In the mean time if you have any questions, just let us know.