empty tagged playlist using hd radio iTunes tagging

Currently I'm running my MacBook Pro (15-inch, Early 2011) with Yosemite (10.10.1) and iTunes 12.0.1, and an iphone 6 running iOS 8.1.1, but I have experienced the same problem using every combination of operating system/itunes/iphone I've had, so it's also happened using Maverick/iTunes 11/an iphone 5 on both iOS 7 and iOS 8/even an iphone 6+ I had for a week.

A few months ago, I bought a 2014 Mazda 3 that has an HD radio with iTunes tagging. I keep having the same problem: the tag transfer seems to work from my car's radio to my phone (the Mazda Connect system says the transfer has happened, anyway), and when I sync my phone to my computer it does create a "Tagged" playlist, but that playlist is always empty. I've deleted the playlist several times and it always is re-created, but never with any song info. I've tagged songs off of several different stations, so it's not a station issue.

In the car, you have to have the phone connected via USB for the tagged song info to transfer to the iphone. I do that using the extra lightning cable I bought to keep in the car. I use the cable that came with my phone to sync to my computer.

Obviously this isn't the easiest thing to troubleshoot being that you have systems for the vehicle, phone, and computer, plus iTunes software. But I feel fairly confident that it's not the car-to-phone transfer that's the issue, but the phone-to-computer transfer. That's why I think the iTunes import forum is probably the right category to ask the question, but I'm certainly open to correction.

Can't find an answer in any existing discussion/article/how-to/etc that's solved this for me. Anyone have ideas what might be happening and how to get the song info to transfer?