I have no doubt it's a firmware issue with the radio.
Looking at it another way, I doubt it's a firmware issue with the radio, or Hyundai's fault. Everything worked just fine at the time the system was designed, using the technology present at that time.
IMO, I don't think it's reasonable in this computer age to buy anything new -- whether Apple, Windows, or Android, etc -- and expect it to be backward compatible with anything older... even months or weeks older.
High-tech companies are in business to create products that move the market forward. They abandon last year's tech like yesterday's newspapers.
Backward compatibility is possible, but it's very labor intensive (read: expensive), and the risk is to fix one "compatibility issue" and create ten others. Not to mention that BC is counterintuitive to the designed obsolescense strategy noted above... Today's lean-built tech companies are finding that resources are better utilized in creating the new stuff, instead.
Problem is we want the latest and greatest AND we want it to integrate with what we already have. The more we have invested in the "already have" ($20K+ cars) the more the angst. We don't give a second thought about abandoning last year's model iPhone for this year's iPhone. But that doesn't mean we throw away our cars to do so. We deal with the consequences, instead.
They don't call them "patch cables" without reason.