I’ll explain the last one now: If you have CNAME records, it will only return one of the CNAME records. If that CNAME record happens to only have IPv6 addresses, people without IPv6 suddenly can’t reach you. While you still can and many others too.
Lesson learned, it’s fixed now. I’ll also suggest a fix: Add a priority option to all DNS records possible, not just MX records. If that’s not possible it’s time to come up with a better solution.
Update: Apparently CNAME records suck so much that a dual-resolve doesn’t work either.