iPhone 5 Bluetooth Audio Problem w/ Car Stereo (Pioneer AVH-P3300BT)

I tried looking around to see if anyone else had this issue, and didn't find an answer.

I have a Pioneer AVH-P3300BT car stereo, and while it doesn't play music via bluetooth, it does have a very nice setup for talking on the phone.

It's always worked fine with my iPhone 4, 4S, and also several Android handsets. It even worked fine on my 4S after upgrading to iOS 6. But now I have an iPhone 5, and the audio quality is just horrendous. I can kind of hear the person on the other end, but according to whoever I'm talking to, my voice sounds garbled and "demonic". The iPhone 5 on iOS 6 is the only device this happens with. Is there a fix for this, or is it at least a known bug? I would hate for my expensive car audio setup to be rendered useless for the purpose I bought it.

The deck also displays other information from the connected phone, such as signal strength and battery level. When the iPhone 5 is connected, it shows a dead battery (even when full) and a completely full signal (which is almost never really true).

I can use the phone with my Plantronics bluetooth headset and there are no sound quality issues there.