I get the same bug on Win 7 64 bit OS. I'm using a Logitech G35 USB headset. It's not a driver issue with the headset as I updated recently.

I'm also able to reproduce this bug whilst in game, having done the temporary fix of alt + tab and starting Teamspeak. If you go into your options in game, then press "Devices", the game audio also drops.

I've also been able to reproduce this sound bug when VOIP was set to capslock. I haven't tested if I can reproduce it after changing the key-binding.