Mac not automatically selecting correct USB device (speakers and Mic)

I've noticed a new problem (that seemed to have coincided with ML).

At work, I hook my rMBP to a Apple Thunderbolt display, to which I have a USB hub plugged in, which connects to my printer, external drives, speakers, and microphone).

Since installing Mountain Lion, when I login, the Mac is defaulting to the built in speakers and microphone, rather than the external/USB ones. (Previously, these devices were automatically active).

Any ideas?