I've noticed a bug with the Nokia Audio Settings on my Lumia 810. If I have the Dolby and Audio Leveling settings turned on for my Nokia Purity wired headphones, then when I use the Bluetooth A2DP car kit (or any other Bluetooth Stereo speakers/headset)... music will skip or cut-out periodically. It's like bumping a CD player that doesn't have a buffer.
Turning off the Dolby and Audio Leveling options in Nokia's Audio Settings panel seems to resolve the problem on all of my Bluetooth stereo devices.