[CLIENT] When client is open, all other audio ceases to work

I just noticed this issue today. Every time the LoL client is open, all my other audio stops working. It seems like something is wrong with directsound - when I had MusicMaker open, it reported that there was an unspecified directsound fail (which was immediately alleviated once I closed the LoL client). I've restarted the client and my PC, but the issue persists. I've ensured that my audio device is not currently allowing exclusive control.

OS: Win 7 Ultimate Audio devices: both Plantronics HD1 headset and XPS DIAMOND 2.0 USB speakers