Wanted to start a thread on this since I haven't found any info anywhere...
My original setup: Rooted, stock rom Droid 1 running Froyo paired to a 2012 Mazda 3 Skyactive stock stereo
My new setup: Un-rooted, stock rom Droid 4 running 2.3.6 paired to the same
Recently upgraded from a Droid 1 to a Droid 4. I previously used my Droid 1 as a media player linked to my car's Bluetooth connection. After the initial pairing when I first purchased the car the phone would automatically reconnect when I turned on the ignition, as well as resume playback where it had left off. I used the stock Music app (Play Music) before and after the recent updates. On occasion it would lag or skip a bit, but this was due to the phone being old and struggling to run in general. I used the steering wheel controls as well as the console radio controls to operate the phone. Essentially the connection had zero flaws and worked great all the time. Bluetooth calling was also perfect.
Since the upgrade calling works perfectly but music has several issues. To start, the Play Music app does not respond properly with the steering wheel controls. If I advance a track on the wheel the phone switches tracks, but then pauses and requires play to be pressed on the phone to restart playback. If you watch the phone screen while pressing advance, you can see that the track plays for a split second before pausing. Additionally, since the phone supports A2DP my car's display should now show track info, however it generally is stuck on either the track time which stays at 0'00", or the word PAUSE (even if the song is playing). Essentially I have to operate the music controls from the phone, thus making the hands free control useless and being rather unsafe as a driver.
I finally realized though that there were two music apps installed stock, Play Music and Verizon's My Music. Using My Music actually corrected the above problems. Playback is continuous between tracks, I can use the steering wheel controls, and track info displays properly. The track time still doesn't work but at least the PAUSE message is gone. The only issue with My Music (which bothers me a lot) is that playback doesn't resume when I restart the car. I have to physically take the phone out of my pocket, reopen the app, and press play. It's a shame that Verizon's added social network sharing garbage takes precedent over having a music player that works properly (or leaving in the stock Gallery app for that matter, grrrr).
I have looked at Mazda forums and found nothing. The Bluetooth profiles installed should be up to date enough for the car's software since other recent phones seem to have zero issues with it (RAZR and Nexus seem to be fine). I know my Droid 1 didn't have much extra functionality without A2DP but it worked. Now I have all the bells and whistles but a lack of functionality. All I can determine is the phone is the cause software wise.
I've tried factory resets, I've paired and unpaired the phone a million times, and I've searched Mazda forums for feedback. I'm not particularly asking a question here, but just documenting an issue for others to reference should they experience something similar. It's frustrating with the amount of garbage software Verizon seems to think we need, that the primary (and most enjoyable) use I have for my phone doesn't work. I love the phone as a piece of hardware, but the software is failing me and making me miss my OG Droid.