It's not strictly a Google Voice issue. It has to do with the way background applications handle sound on Android. Other apps can cause the problem too. It's also the same root cause of random music playback bug. For example if an audio app is paused in the background plugging in a USB cable, which would normally generate a sound, also causes playback to restart. I believe it's a bug that needs to be fixed in the applications and not really an OS problem. Hopefully by now most apps have fixed it.
http://code.google.com/p/android/issues/detail?id=8038