I just got the ERA. So far I like it. I don't experience your issue. Did you have music playing first, get a call, then the music came back on? Did you ever get to the root cause? I'm still in my return window. My wife has the icon hd and likes it.
No. I was talking on the phone via Bluetooth. During the call I would get in the car and connect the phone to USB as I always do, so it could charge. As soon as I'd start the car, music would begin blasting through the headset making it impossible to hear the caller. The options were to change sources on the head unit or unlock the phone, open the iPod app, click on sources and switch from Bluetooth to dock. If I just changed sources on the head unit (since it's easier), I would have to do the other steps once the call ended or the music would play through the headset instead of the dock after the call when I switched back to USB. That isn't safe while driving, so you have no option but to complete the multiple steps on the phone while not being able hear the caller as soon as you start the engine. It should default to dock when in the car, but it doesn't. It should be programmed to know people won't want music to play through they Bluetooth while they are talking on the phone, but it doesn't.
Since it does these annoying things, I prefer to just disable A2DP altogether and prevent them. However, unlike the ICON, voice dialing does not work on the ERA with A2DP disabled. Also, if you're thinking why not just wait until after the phone call to connect to USB, it's because it just delays the inevitable. It will still default to Bluetooth after the call. There was one workaround, but it only worked if you weren't going to use Bluetooth again in the car. You could wait until after the call ended to connect to USB and then turn the headset off before connecting. That wasn't an option for me since I wanted to keep it on for imcoming calls and voice commands for music.
So A2DP is much more trouble than its worth if you use USB in the car and voice dialing doen't work if you disable it. This is why the ERA is useless to me.
Do you have a USB port in your car?